PLEASE HELP A GRANDMA!How do I put previously purchased apps in the kids mode on my samsung s5 phone

[duawama]

I'd like to put apps like Tap the Frog, Angry Birds that I've already purchased into the Kids Mode on my Samsung s5 phone so my grandkids can play. Mainly so no unauthorized in app purchases can be made. I'm totally baffled and feel a little dumb as I'm sure it's an easy fix but PLEASE HELP A GRANDMA!