When Cara Morganstein was a little girl, she insisted that her dolls have real pacifiers and real diapers - imitation stuff wasn't good enough for them.

"I've been in love with babies and kids forever," says Morganstein, who was a mother's helper by age 11 and a live-in nanny for family friends for three consecutive summers starting when she was 13.

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Morganstein grew up to become a certified veterinary technician in the emergency room at the University of Pennsylvania Veterinary Hospital. But her connection to human babies was renewed five years ago, when she met Lindsey Rosenberg and her husband, Brendan Krivda, through the women's parents, who stay at neighboring Shore homes.

Back in the Philadelphia suburbs, the friendship grew - Morganstein, 29, lives in Jenkintown, the couple in Elkins Park. And when Rosenberg gave birth to son Cole in February 2011, Morganstein was there to offer wisdom, like how a good swaddle and the sound of the oven exhaust fan can calm a crying baby.

"Cara is a baby whisperer - little ones just respond to her," says Rosenberg, 35, now a stay-at-home mother. Another child later - Amelia joined the family in July - and Morganstein has become a fixture in the Rosenberg-Krivda house.

The dynamics between a mother and her child's caretaker are often tricky: In pop culture - and so often in movies - the relationship can be riddled with jealousy and battles, mistrust and misjudgment. But in real life, the two often share a unique bond, cultivated by the mutual love of the babies and a similar value system, and often lasting long after the children cease being children. Sometimes, while the nanny is caring for the kids, the mother comes to care for the nanny.

Longtime babysitter Alyson Sherby and Sally Zeiberg still have lunch together, even though Zeiberg's children are past babysitting age - now 17 (Daniel), 15 (Julie) and 9 (Emily).

"I can't even imagine how different my life would have been without this family," says Sherby, 29, of Cherry Hill.

She met Zeiberg and her husband, Andrew, when she was 13 and the couple, then with two young children in Mount Laurel, got her name from a local babysitting registry.

The Zeibergs thought Sherby was "extremely mature and extremely capable," using her as their regular babysitter. When they had their third child, though, Sherby became a part of the household.

"Sally and Andrew reminded me of my own parents and of the way I was raised," Sherby says. "There was just a comfort level."

Zeiberg, now 50, who juggled being a stay-at-home mother with a heavy roster of volunteerism in Camden schools and in Jewish communal life, realized that in some ways, this young babysitter could give her valuable insights into her own children.

"Alyson had an amazing way of helping me to better understand their personalities," Zeiberg says. Sherby pointed out that while Julie was social, Emily really needed alone time, and Daniel was best when he was busy and active.

"I had the advantage of being closer in age to the kids, but also old enough to have some perspective on the stages they were going through," Sherby says. "The wonderful thing was that Sally really welcomed my thoughts - and I welcomed hers about dating, career things, and life in general."

When Sherby's father died in 2008, the two women drew closer. Zeiberg even helped organize the shivah - the Jewish period of mourning when loved ones come to visit the deceased's family.

"Sally was a pillar of strength when I was in a dark place," says Sherby, now a registered nurse in critical care.

It's been a friendship that transcends age.

"She's part of us, and always will be," Zeiberg says. "My children are just so lucky to have someone besides their family who will always love them."

The relationship between nanny Llana Chicosky and mother Jessica Neff is much newer - but it also illustrates the fine negotiation parent and caretaker undertake to establish trust and comfort.

Chicosky, 24 and already a veteran nanny, watches Neff and husband Jason Siebert's 13-month-old Avery two days a week at their Center City home, while family members pitch in on alternate days.

"It has to be the right fit, and this is," says Chicosky of her 12-hour days with Avery. "She's an inquisitive and interesting baby, and I've tried to help guide her parents because they're first-timers and I've had a lot of experience with kids."

Neff, a psychiatric nurse, agrees that it's been a steep learning curve and that she and Chicosky have had some disagreements, especially when it comes to how long to let Avery cry if she's unhappy.

"I persisted," says Neff, 35, who is a believer in comforting a crying child, even when she's just rebelling against sleep.

"In the end," Chicosky says, "the parent's way has to be the way I go. I'm not the baby's parent, and I never forget that."

Chicosky is glad that she and Neff can talk through their concerns. Recently, she was able to suggest darkening the baby's room to help solve a napping issue - something the new parents hadn't thought about.

"We're in a good place now," Neff says.

Finding that good place is a matter of establishing the right fit from the start of the relationship, says Sara Corse, a clinical psychologist with the Philadelphia Council for Relationships and a specialist in work-life balance issues.

It all begins with the interview.

"It's terribly important to ask the right questions," Corse says, "like, 'Why are you doing this work?' and 'What do you see as your duties - and what are not your duties?' "

There must be a clear delineation: Who is foreman, who is manager, who's in charge when? Mothers shouldn't feel inadequate because the nanny "does it better."

And sometimes, Corse suggests, the best scenario unfolds: babysitter and parent become trusted friends.

When Rosenberg underwent foot surgery two months ago, she learned a sobering lesson. Hardly the helpless sort - she was a Peace Corps volunteer, and later worked with the American Friends Service organization to aid victims of the Indonesian tsunami - Rosenberg was relegated to the couch while husband Krivda, 37, a broadcast sound technician, often had to work long days.

"Facing life after surgery, and with two babies and a husband with crazy work hours, was really humbling. Cara became a wonderful friend to me," Rosenberg says.

In fact, Morganstein "was being much more than a friend," which meant that Rosenberg insisted on paying her for her help.

Being in the house together, double-teaming child care, also could seem like a formula for conflict. But each woman insists that it works.

"The friendship is extremely important to both of us, and we always remember that," Morganstein says. "I also clearly understand that I'm not Cole and Amelia's mother."

But there are still gray areas when the two are uncertain about roles.

Morganstein, for example, was upset when Rosenberg wanted to pay her for driving her to the doctor.

"Remember," Morganstein reminded, "I'm your friend. And you don't pay a friend for doing you a favor."

Rosenberg backed down. "The friendship," she agrees, "comes first."