family plan account asking for credit card

[nohorse]

I have an xbox family plan a recently purchased two wp7 phones for the kids. I also gave them $$ for the app store using the "allowance" feature of the xbox live family account. I expected this to allow them to use the MS points to purchase games in the app store. unfortunately, when they try to purchase a game, they get prompted for a credit card. all is sadness. anyone have any experience with this?