iPad can't download apps on my WiFi, but can using my iPhone hotspot

I have a very odd issue - and I can't seem to find an answer.

I bought my daughter (10) and iPad which arrived yesterday. I'd already made her a child account as part of my family sharing, so setting up the iPad didn't take long. The main reason for the iPad is that her school use Google Classroom, and her old Amazon tablet wasn't much use for it.

Once the setup was complete, I went to the App Store, and found Google Classroom. I click GET, which then turns to a spinning wheel for a minute or two, then goes back to GET. It does this with EVERY app. Pretends it's going to download it, then times out.

If I open Safari, I can browse the internet - so it didn't appear to be a network issue.

I spent a LOT of time turning on and off parental settings, asking for permission, age limits etc.

I then decided to restore factory settings and try again. When restoring, it asked me for her password. When I entered it, it timed out. It did this three times - the last one telling me there was no internet connection. Again, I opened Safari and could browse the internet without any issues.

I decided to Hotspot my phone, and connected the iPad to that.

App Store, Google Classroom, GET - it immediately asked me for a PIN, and then sent a message to my iPhone asking for permission. I granted, and downloaded the App. I downloaded the rest of the Google Classroom suite (drive, slides etc) using my iPhone hotspot.

As soon as I go back onto my home WiFi, I'm struck with the same issue - that clicking the GET button on an app gives the spinning wheel for a minute or two, then times out.

I use my home WiFi connection to download apps on my own iPad and iPhone all the time... so why won't the one with parental settings work?!

It's like something is blocking the AppStore when on the parental settings - perhaps on my home network?

Although I've solved the issue of getting Google Classroom on the iPad, having to download apps to it using my Hotspot isn't a workable solution!

Any help appreciated.