Toddlers explore their own and each others' genitals.
They call this game "playing doctor", probably since at the doctor they've had routine examinations of their private parts.
Adults use the phrase as a "cutesy" way to say "sex".
Synonyms for playing doctor
On this page, you will find 30 slang terms related to playing doctor. Some of the top words include: wank, Squeezer, toe buggering, pedophiliac, tiddlers, and 25 more.