On the subject of irregular plurals --
Dad: "Well, there's irregular plurals. Like 'children'. That's weird, it should be 'childs'."
Child: "No. If it was 'childs' it would be weird. The word is 'children.'"
On the subject of health --
"How come they call it a cold? I'm hot." :: opens mouth, grabs tongue :: "I'm even hotter inside, not cold."