Just to give you an idea.

I set up an account for my son two years ago. He is now the same age as your oldest son, 11 years old. Well, I opened an account for him, delegated some HIVE power and set it to follow my votes automatically. The account has been growing. I removed the delegation when it got 250 HIVE power and left it on its own to follow my votes and added to follow the votes of curation projects like Cervantes. I am sure that when he is 15 and I give him the keys to the account he will have enough to start something.

Don't wait until your sons are 15 to open the accounts and do it now. So that when you give it to them they doesn't have to start from scratch.

Regards!!!

!PIZZA