Ask permission to buy is not working for 11 yr old son

I have two sons, ages 13 and 11, who have iphones. I have set up family sharing, and both sons have their own Apple IDs, which they use to sign on to their phones. I'm the family organizer.

When 13 yr old son wants to download an app, Ask Permission to Buy works, and I get to authorize the purchase. The 11 yr old, however, is able to download apps without the Ask Permission to Buy kicking in. As far as I know, both sons' profiles were set up identically when I added them to the family sharing group.

It was my understanding that the Ask Permission to Buy feature was on by default for a family member under the age of 13.

Anyone have any suggestions?

And, does anyone know how to check whether Ask to Buy is turned on for a family member?

I've been through the other questions on this topic in the community, but have not seen any good solutions.

Thanks in advance.

Pete