I once believed the birds and the bees weren't my problem. My husband would expertly field all the tough questions about sex our three sons threw our way: All I'd have to do is stand beside him and nod.

No such luck. When the topic finally came up, Dad was out for the evening. I was loading the dishwasher, and the boys were in the family room watching a nature show. From my post in the kitchen, I heard this serious PBS voice say, "Sex between sharks can get quite rough." A second later our oldest, 8-year-old Sam, appeared in the doorway with a funny look on his face.

I considered distracting him  -- "Ready for dessert, sweetie?"  -- long enough for his father to get home. But we'd always tried to be open about body parts and functions in our house, and I didn't want to freeze up just when straight talk was needed most.

I told him we'd talk at bedtime, and kept my promise. After our usual songs and stories, I took a deep breath and plunged into those shark-infested waters. "So, that show made you have some questions," I said. "Want me to answer them?" I told him the whole story  -- about how males and females make babies together, with the male depositing his sperm in the female. My son was appalled and disgusted  -- but also intrigued.

Variations on "the talk" don't always come up at convenient times or in predictable ways. So be prepared: below, the best strategies for handling the kinds of scenarios that catch parents most off guard.

Your 3-year-old is fascinated by her baby brother's diaper changes. "What's that?" she asks, pointing at his penis.

How to respond: You may be tempted to change the subject quickly, and fasten that diaper even faster, but it's best to be matter-of-fact. "Some parents teach their children the names of every body part except the genitals, skipping them as if they don't exist," says Mark Schuster, M.D., a pediatrician and coauthor of Everything You Never Wanted Your Kids to Know About Sex (But Were Afraid They'd Ask). That can give kids the idea that talking about your private parts is taboo. So instead say, "That's how you can tell the difference between a girl and a boy. It's called a penis. You have a vagina."
Of course, just because you use the correct term doesn't mean she'll get it right on the first try. Nashville mom Laura Hileman once heard her 3-year-old son explaining to his brother, "Boys have penises, and girls have china." And don't be surprised if the question comes up again and again while your little one sorts it all out.