[MrMars]

My son, who has been part of my family plan for several years now has his own bank card. Is there a way, without removing him from the family plan to have his purchases paid for using his own card?

[SwitchBeach]

No.

But he can use that "bank card" to purchase an iTunes card (either physical or electronic) and then redeem the value of that iTunes card in his iTunes account and then his purchases will be charged against that balance first before using your card.