Tonight with your 13 to 17 year old
The prompt
“Is there something you loved doing as a little kid that you'd still secretly enjoy if nobody was watching?”
What to listen for
If they admit to it easily and laugh, they're comfortable holding onto joy without needing it to look mature or cool, a sign they feel accepted as they are, contradictions and all.
If they hedge with "that's so embarrassing" before answering, they may be worried about being seen as childish. Reassure with your tone, not your words, laugh with them, not at the thing itself.
A flat "nothing really" might just mean they haven't thought about it, no need to dig, just enjoy whatever small thing surfaces.
What this tells you
The old joys they're still willing to admit to tell you where they still feel free to be unguarded around you.