prefold wilful toddlers so you can avoid the need to karate chop them across the middle to get them into their carseats
it's hard to describe but if you imagine a newborn sleeping in a tight pile with their knees up, that's the shape you are aiming for
scoop them up, your arm under their knees, and the other round the back and under their arms, sort of roll them in towards you in a tight hug, removing the arm under the knees, fling open car door, lean over car seat and sort of drop them in.....so long as you keep the knees up they cannot spring themselves out.
works well in a two door car if you can step into the space behind the front seat