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Amy Herring has had enough of parents neglecting to RSVP for birthday parties for her three kids. It's happened so often that she now writes "call for directions" on invitations, so parents have to call if they want their children to attend.

Cindy Birmingham's pet peeve is parents who don't control their small children at parties while gifts are being opened. "The birthday child is surrounded by kids ripping at his/her presents," she says in an e-mail. "It makes me NUTS!"

But Christina Brockett's story takes, well, the cake. Earlier this year, while hosting her son's sixth birthday party at a small theater, she was greeted by a father who hadn't RSVP'd. He arrived after the party had begun, toting his 6-year-old and an uninvited 3-year-old sibling. Brockett was surprised to see them, but welcomed both kids to the party.

"As I'm doing that," she says, "he is just kind of like, 'OK, see ya later,' and he leaves." Brockett laughs about it now, but at the time she was frustrated at having to feed and watch over two unexpected guests while hosting a large party in a public place.

In this age of hyper-planned children's parties, it's not just the kid who pokes his finger in the frosting who has become a party pooper — it's his parents, too.

Occasional etiquette missteps are usually greeted with patience. Busy parents don't expect perfection from one another. But serial offenders have some parents steaming, a situation that puts their kids in an awkward position.

If you're a parent or grandparent who spends time on the preschool party circuit, here are some thoughts from the experts on how best to navigate this social scene.

STICK AROUND OR NOT?

Parties often happen in public places, like bowling alleys or gyms for kids. It's a less controlled environment than a private home, so parents of small kids usually stay. Is that expected?

Kate Lawler, executive editor of Parents magazine, says it depends on age: "We generally say that 4 is old enough for the parent to bring a kid to a party and then come back when the party is over."

Parents of older children sometimes stay, she says, if they've offered to help or are friendly with the host. The key is asking the host whether they'd prefer you stay or go.

Greg Byrnes and Craig Handleman, co-founders of the social networking and information site www.ParentSociety.com, agree that the answer is age-specific. But they set the bar closer to age 6, as do readers at www.BabyCenter.com.

"Parents start to leave their kids at parties around 6 or 7," says Linda Murray, BabyCenter's editor-in-chief. "And by 8 or 9 the kids don't want you there anymore."

Also, talk with your child about the party: If it's, say, a ponyriding party, the child may prefer that you're on hand when they climb on the pony for the first time.

Should both parents come? Doting moms and dads with one child may want to witness — and even document on video — every moment of their offspring's earliest partying. But remember: Much as you adore your child, they're not the guest of honor.

SIBLING RIVALRY

Should you bring siblings along to the party? No, say the experts, unless they were explicitly invited. Party events are often priced per child, so extra kids mean extra expense for the host. Also, the party space may not be childproofed, and the presence of extra kids can make an already frenetic party tip into chaos.

Ideally, one parent of multiple kids will stay home on baby-sitting duty while the other brings the invited child to the party, Lawler says. If that's not possible and you can't get or afford a sitter, talk with the host: Either arrange to drop off the invited child or ask to bring additional kids who won't be participating in party events or eating the meal served to guests. (Babies are always welcome and don't require permission.)

THE GIVING TREE

Is there pressure to bring an expensive gift? Experts say it's always fine to bring a simple, age-appropriate present, even if the party is extravagant. (One exception: If you've arranged to bring along a sibling, Handleman and Byrnes say bring a larger gift or two gifts.)

A recent poll of more than 1,600 BabyCenter readers found that 17 percent specified "no gifts" on invitations to their child's party or said gifts were optional. But the majority of readers, Murray says, spend between $15 and $30 on a gift.

You're not expected to give a gift if you decline an invite, says Lawler, "though it may be different if it's a cousin or beloved next-door neighbor."

PLAYING ALONG

If you're at a kids' party, how involved are you expected to get? Byrnes says it depends on what's planned: At places like The Little Gym, a national chain with gymnastic equipment and mats for tumbling, you may be invited to play along with the group. It's impolite to say no.

At most venues, though, parents are simply spectators. If a group of parents is sitting on the sidelines, socialize just as you would at any party, says Lawler. It may seem onerous if you're not in a talkative mood, but it's a great opportunity to meet your child's friends and their parents, and maybe schedule a few play dates.

The keys to this social landscape, Lawler says, are common sense and plenty of communication with your hosts about their plans and what they expect from you. And, she adds, don't forget to RSVP: "It seems obvious, but people do forget."