There is not that type of control, once the Crowns are on an account they can be spent in any way.
We do, however offer the option for you to purchase the Crowns on the Family Master Account and transfer them (in any amount) to the 'child' account. This will allow you to budget out the Crowns as you see fit. Once the Crowns are on the 'child' account, they can be spent in any way, but at least you can only dole out the amount of Crowns you are comfortable with them spending at once.
