The kids gathered in the family room of Cherise Peters's home in Olympia, Wash., enjoyed a typical playdate, as the boys pushed toy trucks around and the girls drew pictures. Typical, that is, until Karen Larsen instructed her children Allison, now 6, and Aaron, 3, to take a drink from sippy cups that had just been used by Peters's children.

Most moms would say that's a good way to spread germs—which is precisely what Larsen intended. She is one of a growing number of parents worried about the safety of childhood vaccinations—including the shot to prevent chicken pox. Larsen opted instead to take her children to a "chicken pox party" after learning online that a like-minded mother, whose children were already infected, would let Larsen bring her kids over so they could be exposed to the virus. Since chicken pox can be serious in adults, Larsen, 32, says she wanted her kids to develop immunity now. Sure enough, within two weeks both had sprouted the telltale red pox and quickly recovered. "You hate seeing your kids sick," says the stay-at-home mother from Auburn, Wash. "But it made sense to expose them naturally."

Once a childhood rite of passage, chicken pox has become less common since the vaccine came on the market in 1995. Today, more than 80 percent of American children—3.2 million a year—are immunized when they are between 12 and 18 months old. But some parents, despite urging from their doctors, balk at the pox shots because they fear the vaccine may contribute to autism or other childhood disorders (see box). Experts say the vaccine is safe—and important: While generally not serious, chicken pox, like any illness, can be unpredictable, and, in a small number of cases, can cause encephalitis (inflammation of the brain) or even death.

But such concerns aren't on the minds of parents who scour Web sites looking for invitations to pox parties. Brooke Liebowitz posted an invitation to a party at her Flemington, N.J., home after her sons Asa, 3, and Seth, 1, broke out in blisters. But what she hoped would be a fun if infectious afternoon became a bit of a downer as one mom wrapped Seth in a towel and then rubbed it on her 2-year-old daughter's body as the little girl teared up. "She was really freaked out—my son looked like an alien," says Liebowitz. "It was a very uncomfortable hour." (But successful: the girl became infected.)

It's no surprise some parents feel awkward. "I think it's really strange and unfortunate that parents would expose their kids to something that can actually do them harm," says Dr. Thomas McCall, a pediatrician in private practice in Littleton, Col. "It doesn't seem like a good parental choice." Perhaps such doubts played upon the minds of parents who read the invitation Larsen posted after her kids got sick. She waited several days, but no one took up the offer. "I did have a few neighbors tell me, 'We'll stay away' " Larsen says.

Nancy Jeffrey. Nina Burleigh and Jennifer Frey in New York City, Stacey Wilson in Portland, Ore., and Vickie Bane in Littleton

  • Contributors:
  • Nina Burleigh,
  • Jennifer Frey,
  • Stacey Wilson,
  • Vickie Bane.