The 5 and 7 seater lost their monopost seats in favor of a 60/40 split bench in the 2nd row to allow for a fold-flat design to increase cargo capacity. The 6 seater remains with the monopost seats in the 2nd row. While the monopost seats in the 7 seater offered a car seat safe tilt for 3rd row access this is now lost with the 60/40 bench. For those needing to put car seats in the 2nd row and preserve 3rd row access in the new 7 seater, note that a car seat installed in the center seat will block 3rd row access from either side (it overlaps just enough into the passenger seat to block both sides from moving) and the vehicle seat will not slide forward for 3rd row access if a car seat is installed on that seat.
The Tesla Model X is available either as a 5, 6, or 7 seater. All 2nd row seats are the monopost seats which move independently of one another. The 5 and 7 seater feature identical 2nd rows. The 6 and 7 seaters feature identical 3rd rows.
The 5 seater model has LATCH in 2D & 2P, and only a tether in 2C. The 6 seater model has LATCH in all 4 rear seating positions, while the 7 seater has tether anchors in all 5 rear seating positions, but no lower anchors in 2C.
We’ve divided up our comments by row – all, 2nd, and 3rd – as there are issues that are unique to the seats in the different rows.
Tether Location & Routing: All seats in the Tesla have fixed head restraints that do not allow you to pass a tether through them – and the head restraints are not removable. Tether straps that are straight (as opposed to the V-shaped tethers found on Britax seats and the IMMI Go) will go around the vehicle head restraint on the side closest to the door. The exception is the 2nd row center seat where a straight tether should be routed OVER the head restraint (apparently the 2nd row center head restraint is designed differently and will bend forward in a crash). 
V-shaped tethers will go around either side of the Tesla head restraints. However, V-shaped tethers do not work well with the very narrow, sloped “shoulders” of the Tesla vehicle seats.
Narrow Seats: All of the rear seats in this vehicle are quite narrow. At 5’1″ and about 120 pounds, I found these seats to be designed for someone my size and imagine that wider individuals will feel cramped.
Shoulder Belt Location:The shoulder belt is integrated into the vehicle seat which is nice when you are moving vehicle seats that you don’t have to worry about getting the seat belt caught – and allows the outboard 2nd row seats to move for 3rd row access without requiring a LATCH installation like other vehicles do. However, I found the shoulder belt to be very close to my neck and uncomfortable in the 2nd row seats (note: it is not dangerous for the belt to rub the neck).
Lap Belt: The lap belt is anchored significantly forward of the seat crack (bight) in the 2nd row seats – which improves belt fit on teens and adults, but will prevent the secure installation of a significant number of car seats when attempting a seat belt installation. This is particularly an issue for the 2nd row center seat as it has no LATCH anchors, so you must use the seat belt to secure the car seat.
2nd Row Center Seat: Since 2C has no lower anchors, you’ll want a car seat that installs well with a seat belt (one that has a built in locking device for the seat belt is key). We’ve found 2C to be particularly well suited to rear-facing car seats… not so much for forward-facing car seats. The Cybex Aton2 is exceptionally tolerant of seat belts anchored forward of the bight and was able to install securely in the 2nd row center seat. The Chicco Fit2 also worked very well in 2C. The Clek Fllo was also a great fit rear-facing in 2C with the anti-rebound bar – and like the Chicco & Cybex, the Fllo allowed both front seats to come all the way back. Since the 2nd & 3rd rows are quite shallow, it can be very beneficial to put the rear-facing child in 2C as this way their seat doesn’t take up any room into the front seats. While Foonf installs securely rear-facing in 2C, it sits so high that you can’t see hardly anything out the rear view mirror (and it nearly touches the roof). 
3-Across: 3-across here is tricky – as the seats not only need to be narrow, they also have to be able to accommodate the bizarre contours of these vehicle seats and the head restraints that protrude forward. 2C is particularly tricky as it has no lower anchors – and the seat belt is anchored in a way that many forward-facing car seats won’t install securely. We’d suggest saving 2C for a rear-facing seat – as you can see below, we used a Clek Fllo which worked great (Clek Foonf won’t work in 2C as the roof line is so low that rear-facing Foonf basically touched the roof).
The Clek Foonf is the perfect choice for a forward-facing seat in 2D & 2P (as well as 3D & 3P) using rigid LATCH + tether (+ seat belt for kids over 35 pounds) for a few reasons:
1. The contour of the back of the Foonf coupled with its rigid head restraint design (as opposed to the flimsy/flexible head restraints on many other forward-facing seats) handles the protruding head restraints in the Tesla without a problem.
2. We know that tethers are less effective when they have to route around a head restraint and as such we wanted a car seat that could hold itself as tightly coupled to the vehicle seat as possible – and rigid LATCH is the perfect solution as it doesn’t let the car seat move side to side or front to back in the same way that a seat installed with a belt (LATCH or seat belt) does in a crash. Note: usually we’d suggest a V-shaped tether (like on a Britax or IMMI Go) in situations with a fixed head restraint, but in the Tesla these don’t work well in 2D & 2P as the severe slope of the Tesla vehicle seat makes it such that these tethers slide too far off to the sides of the vehicle seat to offer much protection – and in fact the Go is incompatible with the Tesla Model X seats.
3. The awkward contouring of the vehicle seat and buckles & seat belt anchored forward of the bight (seat crease) make it a challenge to get many car seats installed securely with the seat belt – and since Foonf allows the rigid LATCH to be used at all times forward-facing (so long as for kids over 35 pounds you add the seat belt in addition) we know we’ll have a super secure installation the whole time the child is in the Foonf.
Trouble with Boosters that use LATCH: I tried a variety of high back boosters in the 2nd row seats and encountered some fit issues. First, the head rest tips forward on all of the Tesla vehicle seats – and since the vehicle head rest is not removable this can cause issues with fit of forward-facing car seats and boosters. You need to read the manual to your child’s car seat or booster to see if they allow or prohibit the use of the seat when there is contact with the vehicle seat only at the very top where the vehicle head rest is and then a large gap between the car seat/booster and the back of the vehicle seat. The Maxi Cosi RodiFix booster, when LATCHed in and used in its upright position, fit best – there was however a small gap between some of the booster and the back of the vehicle seat.
The Clek Oobr booster when LATCHed prevented the seat belt from being buckled. While the buckle was fully visible, you could not fit the metal tongue fully into the buckle… no matter how hard you tried. The Cybex Solution Q-Fix booster when LATCHed was very difficult to buckle the seat belt (but possible). 
The Maxi Cosi RodiFix, when LATCHed, was very easy to buckle the seat belt. 
Besides boosters that have LATCH, the only other time you will use the lower anchors AND seat belt at the same time is with the forward-facing Clek Foonf when the child weighs more than 35 pounds. With the Foonf installed with rigid LATCH it was possible to get the seat belt buckled. Note: the Foonf will need to be in recline position #1.
Seat Recline: Interestingly, the 2nd row seats are a fixed L-shaped seat – and when you recline the seat your knees go up. It is not like most vehicle seats where when you recline the seat only the back rest moves back. The L-shaped seat is likely a safer design as it will help prevent submarining during a crash – which is when people slide under the lap portion of the belt – something which is more likely to happen if you increase the angle between the seat back and the seat bottom.
Shallow 2nd Row: Compared to other SUV’s, the Tesla is not exceptionally deep in the 2nd row – which means that if you have a taller driver/front passenger, you’ll need to be careful when choosing a rear-facing car seat to make sure it doesn’t take up too much room into the front seat. As noted above, a rear-facing car seat in 2C won’t take up room into either front seat – but that isn’t an option in the 6 seater as there is no 2C.
Rear-facing car seats that will take up the least amount of room into the front seat: Cybex Aton2 (rear-facing only seat – will fit most kids until 9-12 months of age), Graco Extend2Fit 3-in-1 (convertible seat – will fit most kids rear-facing up to 5-6 years of age). In the picture below, you can see how much farther back the driver’s seat can come with a Graco Extend2Fit 3-in-1 behind it compared to the front passenger seat with the Peg Perego Primo Viaggio 4-35 infant seat behind it (the driver was 6 feet tall).
Potential for Head Injury: When sitting in the 3rd row, I was most concerned by the fact that my head could easily hit the metal bar that runs along the top of the trunk (the metal at the top of the rear windshield). In a frontal crash, the head and torso move forward and the head could easily contact this very hard, unpadded surface which could lead to a massive head injury. At 5’1″ I shouldn’t be “too tall” to sit somewhere safely.
A 52″ child could not sit safely in the Maxi Cosi RodiFix booster in the 3rd row as the child’s head was too high.
Leg room: The seat pan in the 3rd row seats is shallower than in the 2nd row (which means kids will outgrow the need for a booster sooner in the 3rd row). Finding room for your legs is awkward in the 3rd row as you have to sit diagonally to get your feet to tuck under the 2nd row seat – since the seat in front of you is not directly in front of you, but rather off several inches to the side.
Rear-facing seats in 3rd row: I tried the Cybex Aton2, which is the most compact infant seat on the US market (compact meaning it takes up the least amount of room front-to-back). It is so compact that it even fit in the back seat of a Porsche 911. But, it didn’t fit (when using the base) in the back seat of the Tesla Model X in the 7 seater model…
The 2nd row center seat of the Model X does not move up as far as the side seats do. There was not enough room to get the Cybex carrier into its base when the base was installed in the 3rd row and the 2nd row seats were all moved up as far as they each would go. The Cybex carrier without the base did fit and install securely in the 3rd row – but there was barely a millimeter to spare. While I didn’t try it out, I don’t imagine that any rear-facing convertibles will install securely in the 3rd row in the 7-seater models (it may work in the 6 seater models that don’t have the 2nd row center seat).
