Q: How do I set up allowance accounts in itunes..???

I set up allowance for my grandkids a long time ago.. This year I had to go in and change my payment info and it totally wiped out the allowance and I have looked and looked and aside from the page to edit your personal info I cannot find how to get in and reset my allowances....yet when I click on one of the kids purchases in purchase history it pulls up their name and allowance amount but is not letting them charge against the amount...HELP