When your child starts to get curious about his genitals, is it appropriate to teach him the "correct term" (i.e. Penis)? Or to use euphemism such as "bird bird"?

I advocate for using proper names for body parts. It demonstrates ownership and pride in our bodies. In my experience, I find that when parents trust their children to understand certain concepts after an honest explanation, kids can surprise them with a logical response. At least, one could hope.