Ted claims that if you use narrower car seats, like those made by Diono, you should have no trouble fitting all three of them in the back of an R1T.
It may be difficult to fit three large, wider, convertible seats in the same row of almost any vehicle.
As a matter of fact, Rivian (smartly) has installed three seats in the middle row of one of its demonstration models, reflecting the fact that many buyers will do the same.
Rivian, meanwhile, claims that there are three available ISOFIX anchors in the back for standard-sized car seats.
The need to buy multiple seats is eliminated with the convertible seat's ability to face either backwards or forwards and, in some cases, into a booster seat.
Booster seats with detachable backs are convenient for older children who are almost too big for them.
A child climbs in, the seats fold up and down, the adults spread out across the entire bench, and even the car seats themselves are rearranged (which may be difficult to accommodate 3 across the row in many cars).
When I'm in the third row, I find that the middle seat facing forward provides the most legroom.
If you don't mind, I'd like to give you a test-perspective driver's on the Rivian R1S and explain why it's on my and so many other people's wish lists for a new car.