Mothers say they plan to start asking other parents whether their children have had all their immunizations and, if they haven't, the play date is over.
Nichoel Kimmerle, who was outside the Los Angeles Zoo with her children, said she would "absolutely" tell other parents to vaccinate.
"More people are standing up and saying, 'This doesn't cause autism. We know it doesn't, so you need to vaccinate your children,'" Kimmerle told ABC News. "And I think some of us are questioning schools. How many kids aren't vaccinating in the school, and do I want to send my child there?"
But Oregon stay-at-home dad Chuck Dotson said he isn't budging.
Dotson takes his children to an Oregon play cafe where the owner tells KATU she would love everyone to be vaccinated, but she won't ask unvaccinated children to leave.
Sheri Johnson, on the other hand, told ABC News she's thinking of vaccinating her children after avoiding the shots because her fiance doesn't believe in them.
"I’m thinking about looking into it more just to be on the extra safe side," she said, adding that she thinks it's every family's right to choose what's best for them.
Lyss Stern, CEO of Divalyssious Moms, an 11-year-old lifestyle company based in New York, said the measles outbreak is a hot topic among her half a million members.
"The chatter and the buzz isn't just online," she said, adding that vaccine conversations are happening between parents on playgrounds, in classrooms, in doctor's offices and in restaurants. "You have the right to ask ... the person throwing the birthday party. You have the right to ask if they know who's been vaccinated and who hasn't been."
Measles is so contagious that it can spread to an average of 18 people for every one person who gets it. Because the virus is airborne, it can linger in the air and infect someone after they've left a room, according to the CDC. It can also live on surfaces for hours.
Even worse, measles is contagious long before symptoms appear, according to the CDC.
Nancy Aubry, who stood with her 3-month-old son outside Andi's Daycare in Los Angeles, said the measles outbreak makes her both angry and frightened.
"It's just bizarre that it's 2015 and this is even on the table," she said. "My baby is too young to be immunized and so I feel like we’re at everybody else’s mercy until he’s old enough to get his own shots so I have to depend on others to do what they need to do to protect my little one while I can’t. I don’t think it’s fair that people can make that choice and put my baby in danger."