Place it right after the childish moment, then follow with Nelson's Ha-Ha! to extend the joke, or cut to Sad Violin when you want the moment to turn into mock sympathy for the person being called out.
O tym dźwięku
This is a short spoken clip of about three seconds built around the phrase act your age, delivered as a direct, teasing call-out. It lands with a playful, slightly awkward sting, the kind of nudge that makes a joke feel pointed without turning serious, and it works best when the target knows exactly why they are being called out.