Your kids couldn't have picked a better hobby.
I don't know what part of Los Angeles you are from but most of the old rock shops are gone but since they want to get into making jewelry, "Bourget Brothers" in Santa Monica has everything needed to make every kind of jewelry. It is not the old rock shop type of business but they do have all kinds of rocks and specimens and machines. It is located in the front corner of their construction materials supply business so don't get confused if you go there.
Most all cities and large manufacturing companies in and around LA have rock clubs such as the South Bay Lapidary Society in Torrance which is where I am located. They all have field trips each month, and if you can find a copy of the magazine called "Rock and Gem" it publishes shows put on by these clubs so you can usually find a show in the Los Angeles area almost every weekend. Most of these shows have a tool and equipment vendor. The shows put on by cities in the outlying parts of LA have "Tailgate trips", connected to the shows so they have field trips to areas close by.
When you are just getting started at "Rockhounding" going on guided field trips from a rock show or from a rock club is a good way to go as you will learn about the different kinds of rocks, minerals and fossils. After you learn the do's and don'ts and get the right equipment then you can pick any location from the "Gem Trails" books and go on your own.
Hope this helps,