turn off apple password for child

My child's ipad, which is set up with family sharing and ask-to-pay restrictions, requires his itunes password every time he wants a new app, even if it's free. I can't seem to turn it off, no matter how i try! he is too young to type in a password for his itunes account each time he wants to request an app. The rest of the ask-to-buy is working just fine. One note: the ipad is an old ipad 2 running 9.3.5. Does that affect my ability to not require the password every time?