Can't download app to iPad set up for child

Trying to download a child app to an iPad Air set up for my granddaughter.

She has her own Apple ID and password of course. And I have a password to allow purchases or other adult-approval items.

When I ask App Store to “Get” the app, it asks for her password (specifically displaying her user name). The download circle twirls a few times and then reverts back to the Get button, without downloading the app. Tapping Get and entering password has had the same result many times, with no download. I am never told that the password is wrong or asked for the “adult approval” code.

Help!