"Ask to buy" on iPad problem

[Sofassogood]

Santa brought ds an iPad, and I have set up family sharing with my own. Turned ask to buy on so he doesn't run up bills. For a while it worked fine, with notifications appearing on my iPad and iPhone (though if I accidentally swiped them away there was nowhere I could find it again).
But the last two days he makes a request, I get no notice of it at all. I can still go on his iPad to approve by typing in my own username and password.
I've googled this but only really saw the suggestion to log us both in and out of accounts, which I have done.
If anyone has more experience, would be great to hear your suggestions!