Number one among children?

• Kindergarten whiz?

Wiktionary Word definitions in Wiktionary
alt. 1 (context uncountable baby-talk English) urine. 2 (context countable baby-talk English) The male or female sex organ. n. 1 (context uncountable baby-talk English) urine. 2 (context countable baby-talk English) The male or female sex organ.

Wikipedia Word definitions in Wikipedia
Peepee or pee pee may refer to: Pee Pee Creek , a stream in Ohio Pee Pee Township, Pike County, Ohio The Phi Phi Islands in Thailand are sometimes referred to as "Pee Pee Islands" because that is how the name is properly pronounced Slang for penis or urine ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1923, childish reduplication of pee .