It started as joyous praise when we changed his diaper. This was a few weeks ago. He would grab himself and shout, “My penis!” with gusto. I noticed something similar with our first son, but not with this much vigor.

Still, this should be handled maturely, even with a boy not-yet-2. Like many others, my wife and I believe in using proper names for body parts, as well as engaging in the inside voice/private parts discussion. (See this related Moms and Dads blog on this subject.) So I would say, “Yes, that is your penis, but that is private.” And then I would try to finish changing his diaper with a straight face. Difficult.

Then, he stopped. I thought the stage was over.

The other night as I changed him, he grabbed himself again. But this time, with his language developing, he could elaborate. He has two new words these days -- usually reserved for cars and trucks -- “big” and “huge.” Hence, he shouted, “My big penis.” And then, “My huge penis!”

What do you say to that?

Here’s what some experts say. “For the toddler, explorations of all kinds are normal,” write the authors of What to Expect: The Toddler Years. They make the point that, for toddlers, their private parts have been “largely out of [their] reach – under wraps, so to speak.” Our youngest isn’t out of diapers yet, but he’s realizing that he will be. What to Expect also offers a tip: if their hand is wandering in public settings, and it makes you uncomfortable, try distracting them with an activity such as blocks. And engage in the public vs. private discussion.

The New York Times’ Jane E. Brody wrote on a related topic this week in a column about the importance of talking with children, and providing them with the correct names for things, including body parts. “Avoid 'baby' words and baby talk, which can confuse a child who is learning to talk,” Brody writes. (This column will also make you think twice before listening to an iPod at the playground with your kids.)

This advice reminds us that, while these moments prompt some inevitable laughter and perhaps discomfort, they are crucial for your children. It’s not enough to say, as I did, “well, that’s private.” That's really just a starting point.