They’ll tell you everything. Almost.If you’re between...

They’ll tell you everything. Almost.

If you’re between 9 and 18 years old, you can go to the Glendale Adventist Medical Center, 1509 Wilson Terrace, from 5 to 9 p.m. Wednesday and learn how to be a baby-sitter. The $10 fee includes materials and refreshments. Preregistration is required. Call (818) 409-8100.

They’ll train you in first aid and CPR, teach you how to get at least some of the green stuff in the little jars down the baby’s throat and, probably, let you practice the old one-handed diaper wrap with the ringing phone in the other hand.

Child’s play.

What they won’t tell you is that once a year--tonight, as a matter of fact--something weird happens.

Kids who are a little older than babies . . . well, they mutate. They sprout warts, fangs, surgical stitches, shimmering veils of ectoplasm. They turn into ghouls, skeletons, witches, Ninja Turtles and Freddy Kruegers.

If you call Ghostbusters, the line will be busy.

If you dial the Exorcist, he’ll put you on hold.

The only solution, if the little monsters you’re riding herd on are 5 and older, is to take them to the Halloween Haunt at the Glendale Public Library, 222 E. Harvard St., from 6:30 to 8:30 tonight (free).

Or the Kids’ Costume Contest at Eagle Rock Plaza’s Center Court, 2700 Colorado Blvd., Los Angeles, from 5:30 to 7:30 tonight (free; registration starts at 5 p.m. Prizes will be awarded for funny, scary and original costumes.

What about those other apparitions? you ask. The ones who ring the doorbell, spook the cat, giggle familiarly at the jack-o’-lantern in the window and howl, “Trick or treat!”?

Better stock up on goodies.