The key to using the balls with the little ones is to make sure the ball is almost taller than they are so that they can't end up laying on the top of it and going over on their head. We balance on the balls only with my help.
I have some of those foam squares that are a foot ie the smaller ones. If you put those into a row and change directions so it goes around they will walk on them sort of like an early version of walking on a balance beam because they sometimes even have trouble staying on the 12 inch wide version.