New iPad will not download apps.

Start here:

If you can’t download or update apps on your iPhone or iPad – Apple Support

If you are experiencing difficulties with adding or removing Apps to/from your iPad, you need to check your ScreenTime restrictions:

• Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Adding Apps - ensure that this permission is set to Allow
• Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps - ensure that this permission is set to Allow

Did you set up a payment method in the Settings app under the main, top ID block/panel, under Payments & Shipping?

Did you create their Apple IDs under a Family Sharing group you organized?