Uninstall program from 2nd user

While I was away, my hubby installed the game "roblox" on my son's login on our iMac running OS Sierra. I need to uninstall it because I hate this game and wish it never existed. I can't seem to find it on the admin user which is me and I have full access. On my son's log in, there is a lot of limited access. I can't even remove the icon from the task bar. It doesn't appear in the applications list. Where is it? How do I get rid of it? What can I look for?