A while back Heidi, a woman from my church, asked me to babysit her 4-year-old daughter Kaitlyn for a couple of hours every Monday while she worked.

One day when I showed up, Kaitlyn couldn't keep her hands of Heidi's tummy.

Heidi tried to distract Kaitlyn. I pretended not to notice.

Then Heidi closed the door. And before 30 seconds passed Kaitlyn whispered to me, "Mommy's pregnant! But it's a secret."

Awk-ward.

That night Heidi sent me a Facebook message: "I am only about 6 weeks along so that is why we have only told a few people," she said. "Please don't tell anyone."

Heidi later explained that a friend of hers became pregnant with twins before she found out she was expecting. Heidi and her husband wanted Kaitlyn to learn about the pregnancy directly from them – not an overheard phone conversation. Besides, Kaitlyn knew something was up and they didn't like sneaking around behind her back.

"She was asking, 'Mommy, what's going on?' " Heidi recalls.

You might have decided when to tell your friends, your parents and your cubicle buddies you're expecting another baby. But when should you tell your kids?

That's up to you. But experts offer a few pointers.

Is your pregnancy viable?

Tragically, an estimated 15 to 20 percent of pregnancies end in miscarriage, according to the American College of Obstetricians and Gynecologists. That's why some psychologists suggest waiting to tell your children about your pregnancy until you're reasonably sure you'll carry the baby to term.

How do you feel?

Your kids will undoubtedly have questions about the new baby. You and your partner should digest the news yourselves before sharing it, says Dr. Margret Nickels, a clinical psychologist and director of the Center for Children and Families at the Erikson Institute

"You want to be sure that you're available to support the child in their questions, in their excitement," she says.

Whom do you want to know?

Nickels advises against sharing the news with your children until you're ready for the world to know. "I would think it would be too hard to keep this information a secret," she says.

But Dr. Irena Milentijevic, a Houston-area psychologist who specializes in women and young children, says it's OK to tell your kids about their new sibling before you're willing to tell your boss. This is a chance to teach your children about subjects that are discussed in private, she says. At first, Milentijevic says, you might allow your kids to talk about your pregnancy with you, your partner, Grandma, Grandpa and no one else.

Have your kids noticed?

Wondering if your children even know you're pregnant? Milentijevic says even toddlers sense something's different. "Maybe Mommy's more tired and nauseous and preoccupied," she says. Explain why in terms your kids can understand.

Nickels, however, thinks kids too young for preschool don't need to be told right away. "A 3-year-old will actually not notice that Mom is five months pregnant," she says. If you're not on bed rest and can still carry your toddler around, she says expecting the child to anticipate a new sibling's arrival for several months is a bit much.

Either way, Nickels says, share the news with all of your children at the same time.

And if your child hasn't started talking? Tell about your pregnancy anyway. Milentijevic says a baby doll could illustrate what you mean.

Heidi (now mom to baby Meghan) says she has just one regret about the way she and her husband told Kaitlyn about the new baby: They didn't capture Kaitlyn's joyous, feet-kicked-in-the-air reaction on video.