Tonight with your 5 to 8 year old
The prompt
“What's the silliest rule for tag you've ever heard or made up, like everyone has to hop, or the ground is lava?”
What to listen for
If they light up rattling off rules and invent new ones on the spot, that playful energy is them showing you they feel free enough to be silly and creative without worrying about doing it "right."
If they mostly repeat rules from friends rather than inventing their own, that's totally fine, notice if they seem to want you to invent one together, which is really them asking for playful connection more than a rule itself.
If they say "I don't know," start making up a silly rule yourself and see if they jump in to top it.
What this tells you
How freely they play with this question shows how comfortable they feel being silly and creative around you.