Snorkeling in California

Try google for snorkeling in La Jolla and San Diego. There are places for snorkeling there.

If you want to make a weekend out of it, you could go to Catalina. For those readers who don't know where Catalina is, it is an island 26 miles off the coast of LA/Long Beach.

Snorkeling along the coast of CA is not terribly popular as the water can be quite cold and, in many places, the ocean is rough, rocky, and not really clear enough to see anything even if it were safe enough to go in.
That said, the best place is La Jolla, just north of San Diego. There is an underwater marine park in a cove, La Jolla Cove, that is popular for snorkelers. If you can hit it on a clear, calm day then the snorkeling is pretty decent. Don't expect it to be anything like you would see in Hawaii or other tropical places but it might be a nice introduction for your kids!
I have snorkeled off of Laguna Beach around the rocks there but wouldn't recommend it for inexperienced snorkelers since the current can be strong. I've also gone snorkeling and scuba diving in Catalina but that is done off of a boat and I don't know if you would be comfortable having that as a first experience for your kids.

Maybe I'm reading between the lines here, but if your intention is to familiarize your kids (what ages?) with the equipment before taking them to a tropical destination to try it for real then your best bet would be to do it in the controlled environment of a local pool. Per Anita, the California coast wouldn't be my first choice as a beginner either - generally challenging conditions plus water temperatures that would make the average Hawaiian scream.

Gotta agree with the above. Best place in California for first-time snorkeling for most kids (and adults) is gonna be a pool.

If you want warm, clear water with interesting things to see...you will want to try someplace considerably further south - like Mexico.

We snorkeled in Catalina (wearing wetsuits). The bright orange Garibaldi fish would be a hit with kids.

I have fond memories of learning to SCUBA dive as a teen at Santa Catalina Island. You will definitely need wet suits, even in summer, but there are fish sanctuaries (areas roped off from boaters) that would be great for snorkeling. There were dolohins, seals, large schools of fish, and yes, the jeuvenile garabaldi were my favorite!

We also snorkeled in Catalina ( Avalon) for an afternoon when our cruise ship to Mexico had to quickly create a new itinerary (H1N1 breakout in Mexico)

We love to snorkel, and scuba dive, and it was ok there. We had to rent a wet suit we saw lots of big fish, but I wouldn't have called it good snorkeling. But, we were just offshore not far from town.

Funny you said that. Because that's exactly what we ended up doing. Just got back on Monday.

I went from terrified to water to scuba diver in a few years. I prefer learning in baby steps myself, but push yourself. As another blogger said, buy a cheap snorkel kit and practice in a pool of available. I will be snorkeling Mission Bay San Diego in a few months, there are calm places. Be prepared for crowds, wear appropriate water/safety gear. Have fun, I've found underwater to be fascinating, even if not the colorful Nat Geo experience we were expecting.