I've got a childrens bank account set up for DS, and I've put a lock on withdrawls. It's pretty high interest too, and for only 16 months old, he's already for $225 in it. What I'm about to start doing (because I get paid weekly for now) is set up a direct transfer for $10 a week. I'm going to go into the bank in the next few days and see if theres a way that I can make is so he can't access it until he's 18.
I'm probably not much help, but thought I'd tell you what I do