When my kids were in nursery school and elementary school, I'd drive a carload of kids on field trips and none were in car seats or booster seats. I guess there are no parent-driven field trips for 8-and-under kids.
When my now-adult kids were in elementary school, I drove for a lot of field trips. I had a 7-passenger van with bucket seats that could move around and spin, making my van a popular field trip vehicle. Talk about a nerve-wracking drive, sometimes 1 or 2 boys would unbelt and move around inside and I had to scream at them to sit and fasten their seatbelts. And this was while driving on the freeway or on mountain passes. Never forgot one name, Thomas, who was a brat and always disobeyed.