Puzzling issue on new ipad

Having been given an ipad for my birthday, my wife has had one for some time before I decided.
However my grandson (8 yearold) likes to play with my wifes and has a habit of downloading game apps (free ones I should add) we often delete them when he has gone home.
Oddly however these apps are also appearing on my ipad which my grandson has no access too.
How can I stop this from happening please ?Please Help. Thanks !
I didn’t find the right solution from the internet.
Explainer Video Examples

If both your iDevices share the same Apple ID, what you download on one device will also appear on the other device. I see an app I like, I download it on my iPhone and it also shows up on my iPad.