I have £20 iTunes credit but whenever I try to make any purchases it tries to charge the head family member - how can I spend my credit without this being charged to them?
It should do it automatically. I have my family set up that way as well. I'm the head of the account, and have my credit card on file, but my 12 year old daughter has her account as part of our family as a child account, and we get iTunes gift cards for her and keep a credit on her account. When she requests something, I approve it, and it automatically deducts from her gift card balance, and not off my credit card.
I'd contact apple support and have them look into it.