I once played my younger brother to 50 wins (whoever got there first was the unquestioned champion of RPS). It got very, very meta and there was drama in every round. We would pace around planning the next move and then meet up and shoot. An unexpected outcome after that much planning and pressure created some hilarity.
Long story short, I beat him 50-28, so I do feel I was out leveling/reading him to some degree. Maybe some obvious pattern I picked up on but didn't notice.
Ps, we were both adults. Great game though.
Maybe design some kind of goofy little arena for them. Let them dress up in costumes. Put some medium stakes charity donation on the line. An announcer and color commentator calling the match.
I wanna see Ken Jennings take on Annie Duke. Dennis Rodman battle Sebastian Bach.