iPads are known for not having much storage. So, after a while, taking pictures will mean you come across problems when attempting to download and install apps.
You may find that even after deleting pictures on the iPads - you still don't seem to have any storage available.
This is usually caused by the deleted pictures still being in the recycle bin. Follow the below steps to solve this problem.
1. Open the Photos app.
2. First, delete any photos that you want to get rid of.
3. Then, to empty your photo trash, tap on "Albums" along the bottom.
4. Scroll down to tap on "Recently Deleted" (should be at the very bottom). This will open the Recently Deleted album.
5. Tap on "Select" in the upper right corner.
6. It will then ask you if you want to completely remove them from your iPad by hitting "Delete All.