Yes, it is THAT joke!
The girl and the flagpole:
Boy: I’ll pay you 10 bucks to climb up the flagpole.
Girl: Okay. (climbs the flagpole)
Girl: Mommy Mommy a boy paid me 10 bucks to climb the flagpole.
Mom: He just wanted to see your underwear!
(Same boy): I’ll pay you 20 bucks to climb the flagpole!
Girl: OK thanks! (climbs the flagpole)
Girl: Mommy Mommy today the boy paid me 20 bucks for climbing the flagpole, but today I tricked him this time I wasn’t wearing underwear.