Sometimes, it's just the way the questions are written that make them so funny. Such as the following:

"So when you have sex when you're 40, the eggs get too old?"

"If 2 men have sex with a woman, can it make a child?"

"What happens when you suck a girls boobiez?"

Anytime you use the word, "like" in writing, it makes everything sound funnier: "What if you have twins and they are stuck together! Like head to head?"

Or, my personal favorite:
"If you suck a penis (spelled wenuis. Remember the PPP Penis story?), will a sperm still fly in your egg?" I had to emphasize the word "fly."