LF fic with specific secret child specific trope “how old are you?”

You know the moment in a secret baby/child trope where they run into the kid, and the dad asks “how old are you?” And the kid tells them, and they figure out that way that they’re the parent? I want that!!

This rec brought to you by that exact moment in once upon a time (the tv show) with Henry and Emma, and Henry’s dad.

I know this happens in aparecium, but are there any more? HEA only please, but that’s my only request.