Certain things remain constant: the balloons, the ice cream, the cake, birthday candles, slightly askew, dripping wax onto the frosting. Also constant are the pitfalls of giving a child's party.

Following is advice from five mothers who have found themselves in the pits and ideas on getting out:

Never ask more children than you can handle. Children with winter birthdays usually want to ask the whole class.If it's too much, avoid hurt feelings by being a sexist; invite only the boys of only the girls.

What seems like a good idea -- inviting the mothers to help -- usually isn't. You wind up giving two parties, and children who might be slightly awed by the stranger in charge feel no such restrictions when it's Mother .

Set a definite time for children to be picked up unless you want extra guests for dinner.

Play games where there are no losers. Prizes for all.

No fancy foods. The children won't eat them.

If you live in a small place, give the party in a park. Or invite several of your child's friends to an arcade featuring pinballs and electronic games and give them each rolls of quarters.It's still cheaper than a large party.

One woman arranged to make a contribution to the fire department of their small town; in return, the children were allowed to play on the engine for an hour.

Other ideas:

A fish and chips party where they got to eat out of newspapers rolled into cones; a magician; puppets; a storyteller, dressed up in a gypsy costume complete with crystal ball who told the children stories.

The Yellow Pages are a good place to look for magicians, clowns, storytellers, even a dog trainer to set his dog through hoops. Call theaters or theatrical agents for recommendations.

Some area public libraries offer feature-length films to check out. If you book far enough in advance you can have a movie party.

The Insect Zoo at the Smithsonian's Museum of Natural History, open from 10 to 5:30 p.m., could be followed by a picnic on the Mall.

The Discovery Theater in the Arts and Industries Building has a new show each month: puppets, mime, a program to introduce children to jazz. The theater has group rates of $1.25 per person for 20 or more, or you can buy a punch card with 12 entries for $18 and use them all at once or a few at a time. Individual admission is $2.25 for adults; $1.75 for children. Call 357-1500 a month in advance for reservations.

The Washington Dolls' House and Toy Museum, 5236 44th St. NW, (244-0024), offers a tour of the museum, followed by a party in the birthday room, and a session with the wind-up toys. The noon party with sandwiches, lemonade, ice cream and cake is $10.50 per person and the afternoon party without sandwiches, is $8.50. There is a minimum of 8 children and a maximum of 20.