why does my child's device require its own valid credit card even though he is connected to family sharing?

Did one of the most recent software updates mess up the family sharing for kids accounts? My son use to be able to download free apps after I was sent a notice to authorize and for app purchases I was sent a notice to authorize and that is all that was required and my card on file to my account was billed. Now my kids can't download anything with a cost until a credit card is entered onto their device. I'm not going to enter my credit card on their device for them to purchase at will. It use to be connected to mine and now it's not. What's up