Some parents the moment they give birth to a child they open a bank account for the child so that every month from their income they put some fraction of money to the child's account. Some money been given to the child during his birthday celebrations and other ceremonies or visit they always put it into the child's account in other to secure the child's future.
The parents always thinks right about their children and your idea is good but in our country bank account can generate only when the child reach to the age of 18, so for infant there will be no opportunity for the creation of bank account.
The idea of bitcoin investment is good one but the children of this era are so impatience and I don't think that when they hear about it they will keep that money save, instead of saving it for lengthy time they will sell bitcoin in bear market. I think that before going to the Age 7 they should give a lesson about bitcoin so whenever they comes in a reality so they will easily understand each and everything about investment in Bitcoin so their decisions will always be right and profitable.