SO IT'S A DREARY SATURDAY and you've had it up to your earlobes with museums, matinees and malls. The kids are bored. "What are we gonna do, Dad?"

It's times like these that shake the confidence of any self- respecting parent. Quick, before mutiny breaks out: Do I tear the kitchen apart concocting the most extravagant gooey glop to pacify the little munchkins? Or do I capitulate, resolving to play Uncle Wiggily and Candy Land in tandem with a three- a six-year-old for the 1,498th time?

The answer comes from one Henry David Thoreau (or was it Benjamin Spock?): "Simplify, simplify." One activity that fits that mold and always gets us through such days is creating our own homemade radio shows.

Radio? In these days of MTV and all-night sales of VCRs and video discs -- radio? Yes. It's fun and it's simple. It requires no lights, no costumes, no camera -- just a tape recorder, you, the kids and maybe a "special effect" or two.

I usually drag out the portable cassette recorder for this. Simple to use, it also has a built-in condensor microphone that the boys find a lot less intimidating than a hand-held microphone. Recording quality is generally plenty good enough for this kind of fun, and if yours is one of those "boxes" with a couple of speakers, the playback is amazingly good.

Kids are fascinated with hearing their own voices coming out of a speaker (just kids, right?). Playing the tapes back over your stereo or even over your portable recorder gives them a chance to feel close to the big-time.

Getting started: The first few times out, forget about making elaborate preparations and sound effects. Grab a tape, jam it into the recorder. Grab the kids and place them near enough to the recorder that the mike will pick up their voices. And then begin telling stories. (Don't forget to push the record button, or you'll never get them to try this again!)

We take turns telling. The first couple of "sessions," Dad had to take the plunge first. Okay, so your middle name isn't Aesop. Reinvent "Goldilocks" and insert the names of your own gang of bears. Kids are not overly critical. After they've had a chance to watch you record your story and hear it played back "on the radio," they'll warm up to it quickly.

Younger ones may need to be prompted a bit. My first tapes with Matthew, our three-year-old, are distinguished by Dad's frequent "And then what happened?" comments. Six-year-old Benjamin, on the other hand, can wax forth on dragons and castles and monsters for a good eight, ten minutes at a time.

Don't try to do an hour-long recording session and then play all the tapes back at once. Quick reinforcement by letting your "stars" hear their own story played back after each has a turn seems to keep them interested for much longer. Ad that's the whole point, right?

After a few afternoons of this, you might want to get sexy with some sound effects. Again, keep it simple. Blowing through a straw into a glass of water makes great bubbling "lava." Shaking a sheet of flexible plexiglass or metal can roll out a wonderful moment of thunder. Even jangling a large ring of keys can emulate ghostly chains. A lot will depend on your own kids' fantasies and imaginations. And remember that the human voice works best of all.

So give it a shot. It's simple, it's fun, and the tapes are great to save and use to blackmail your 16-year-old in front of his date years later. ("Tommy, remember the time you pretended that you were the radish that ate Washington?") And who knows, you may give the world another Rudy Vallee.