Hello!
Oh no, sorry that happened! I know that can be a horrible feeling when your photos disappear. Sounds like you might have had iCloud Photo Library enabled on your iPhone and son's iPad. With iCloud Photo library enabled, if you delete a photo from iCloud and all devices signed in with the same Apple ID.
Get help with missing photos
Get help with iCloud Photos
How do I delete photos and videos from a device using iCloud Photos?
If you want to remove photos and videos from all your iOS devices, your Mac, and iCloud.com, you can delete them in the Photos app.
When you delete a photo or video from your Photos app, it also deletes from your iCloud Photos and iCloud storage. You can recover your photos and videos from the Recently Deleted album for 30 days.
It also sounds like it could be Photo Stream as well:
When you delete a photo from My Photo Stream on one device, the photo is removed from Photos and iCloud. The photos that you import from My Photo Stream to your other devices won’t be deleted.