Here's a good article about adding belts to a '57:
https://www.thebugshop.org/bsp57_10.htm There's a lot of people who believe lap belts are not much better than no belt at all, with lap belts the risk of abdominal injury in greatly increased. I think its now law that new car manufacturers even have to put a three point belt in the center of the rear seat because lap belts are not much good.
Some purists don't want belts of any sort in their car, I personally don't have a problem with belts if it means the kids can ride in the car safely.
Rob Amos
Happiness is a stock VW