Is it possible to allow children to use different payment method?

My son would like to use his debit card for Apple purchases in the App Store. He is in our family plan and we use screen time with him.

on his phone the Edit option under payment is grayed out. In screen time settings, he is allowed to make account changes.

I tried adding his card to our family account on my phone, but that did not allow him to use it (unless it the default payment method).

is there any way to allow him to use his own card?