I have 4 kids, the two youngest being my boys, who are 4 and 6. Well, recently my 4-year-old interrupted my husband in the bathroom and commented, to anyone who would listen, that his stepdad "had a BIIIIIIG wee-wee!"
This was followed by him wondering about MY body parts, and so he asked me if I "had a big wee-wee." I had to explain to him that "Girls' wee-wees don't stick out." Fortunately he accepted this.
Finally, he got to the point of showing off his penis to me, saying, "When I get big; I'll have a big wee-wee!"
This was followed immediately by him pointing to his scrotum, and asking "What are these for, Mommy?" Fortunately his older brother overheard this and came to my rescue. Very calmly he explained to his brother: "That's where your pee-seeds are. The pee-seeds make pee, and then it comes out your wee-wee." Since he was half right, I decided to let the matter stand for now.
A childhood belief about rude bits

others believed things like this
- Long grass with black seeds were really ant hotels, and the seeds were sleeping ants.— angelsheep
- In primary school, a whole bunch of kids including me believed that watermelon seeds contained ants. — Caff
- I used to believe that condoms were weared by girls and boys
both. And they both have penisAnon - Eating watermellon seeds will make you grow a watermellon in your belly.Anon
- my brother (10) still believes that if you stick your finger to far up your nose you can touch your brainAnon
- my husband believed, until recently, that the word "several" meant seven of something. — sheryl