You might want to double-check that. I was looking at a thread specifically about 3 carseats in the back of a Model 3. There are several options.

You might need new carseats.

But I managed to get our 3 kids in the back of my first generation Nissan Leaf, which I think is slightly smaller.

The 1st generation Leaf was larger inside.

I like the Leaf's interior much more than the Model 3. (But, overall the Model 3 is a much, much better car.)

The first gen leaf is higher, for sure, because it's almost a crossover like the Model Y (and this is nice for loading and unloading the kids, altho it hits the efficiency slightly), but I'm really not sure it's any wider. You really can fit 3 kids abreast in a Model 3.

Look into the Radian and the Clek. I’d be surprised if they don’t work.

(Exciting!)

I do wonder how many techie parents are waiting for the 7 seat Tesla before getting their third or fourth kid.

Congratulations! Driving a van sounds like a good choice when everyone has to go.