It's every parent's queasy paranoid fear come true -- the idea that "the hand that rocks the cradle" belongs to an unstable baby sitter.
Some people have resorted to the "nannycam" -- hidden video surveillance to watch what happens when they're not there.
Now a New York assistant district attorney and mother of two on maternity leave has come up with a new way for parents to spy on their caregivers in the open.
Just like the "How's my driving?" signs you see on 18-wheelers, the Web site HowsMyNanny.com allows citizens to report bad baby-sitting by e-mail.
For $50, you can attach a new "license plate" with the Web site address on it to your child's stroller.
It can turn anyone on the playground or the street into a potential informant.
Some moms say if a sitter has nothing to hide, she shouldn't have a problem with the plate.
"I think it is a good tool because you're being open about it and honest about it, and your nanny knows it's there," said mom Erica Best.
Baby-sitter busting is all the buzz on "mommy blogs," and even was a recent hot topic on "The View." Host Elizabeth Hasselbeck didn't hold back when she saw a baby sitter behaving badly.
"My camera phone wasn't working so I couldn't get her picture," Hasselbeck said. "So she has a purple tank top on, long hair, two babies -- adorable -- and they should have been being watched."
In a "Primetime" experiment, an actress posing as a baby sitter pretends to mistreat the kids she's watching.
Undercover cameras watch to see whether people who see her take action.
"You can never be too careful, so why not have this extra protection, because it can't hurt you. And especially if your nanny's doing something good, it could benefit her," said the Web site's creator, Jill Starishevsky.
Could It Backfire?
But some moms worry about the quality of the reports they might get.
"I don't think it would be that reliable information," said parent Donna Gitter.
Some parents say it's not a good parenting tool -- it's big brother on the playground, and it doesn't foster trust between baby sitter and parents.
"It makes me sick to my stomach, but I kind of understand it," said dad Gunnar Jensen.
"If you don't have the fundamental trust in your caregiver to begin with, it's probably not gonna make that big a difference. Certainly I would love to be a fly on the wall sometimes," said Sarah Haddad.
Many sitters interviewed were sympathetic.
"I can understand the parents side. It's her kid so she wants to make sure her kid is safe. So you wouldn't be insulted. I'm not sure, maybe a little," said Victoria Balogh.
But they were not all happy with the idea of having one of the bumper stickers strapped to their own stroller.
"You either trust me or you don't. That's how I see it," said nanny Sandra Sebro.
All of which is tempting for control-freak parents, but aggressive paranoia could backfire, warns Carol Solomon, director of the New York Nanny Center.
"You have to model the way you want her to be with you on your own actions. How would you feel if you had a camera at your desk?" Solomon said.
How to Check on a Baby Sitter
How do you make sure you're hiring someone safe and reliable, and what do you do if you suspect something is wrong?
Get several references, both work and personal. And contact every reference to see if they check out.
You might consider doing a real criminal background check. There are several services online.
Make sure the person is healthy. Ask for proof of a recent physical, including a tuberculosis test.
Parenting expert Ann Pleshette Murphy says trust your instincts. If you really think something is wrong, just fire your baby sitter. But if you have a vague suspicion, ask people you know who see the sitter and child together their impressions.