The story
Probably a reduplication of pee, but compare French pipi, German Pipi, Italian pipì, Latin pipinna, Romanian pipi, Spanish pipí, Turkish pipi, Greek πιπί (pipí) and North Levantine Arabic پپّيه
Etymology from Wiktionary, CC BY-SA 4.0.
pee-pee
pee·peeToday it means: Urine. Full definition →