Hey there svala50,
We'd like to help look into what may be causing Procreate to not show as a request on your parents' devices. To start, we wanted to make sure you all had the Approve what kids buy with Ask to Buy resource.
You mentioned already updating all of your devices, but the latest is iOS and iPadOS 14.3. You can verify which version number is installed within Settings > General > About. Here's a link that'll show how to first back up, then Update your iPhone, iPad, or iPod touch.
If you three have version 14.3 installed, have you already tried a restart of all three devices? If not, check out how to Restart your iPad and how to Restart your iPhone.
If the issue remains, and as other apps are working with Ask to Buy except for Procreate, the next step would be to reach Apple Support here: Get Support
Take care!