Hi J., good for you for wanting to teach your son now about good money management!!!
We had a 50/40/10 rule with my son. Half went to savings, 40% was his to spend however he wanted, and 10% went to charity. This applied to all the money he ever received -- birthday money, Christmas money, tooth fairy money, money from mowing lawns & raking leaves and eventually from part-time jobs when he was a teenager.
My son was very conservative in his spending, and about 1/3 of the time he would put more than the required half into savings. He understood that once it went into savings, it did not come out until he graduated high school.
He just started college and has over $9,000 in his savings account. At first it was difficult to be strict about the rule, and I am sure there were a few times when we let it slide, but for the most part it became a habit, like going to bed at a decent hour.
The trick is to be pretty consistant and once there are a few hundred dollars in the savings account, kids start getting excited about adding to the account. Good luck and again, hooray for being such a responsible parent!