As you probably know from reading this blog, I'm a big fan of participating in focus groups and usability studies. My kids have participated as well. Here are two local companies that look for kids to test toys. If interested, you can register on their website to get notified of testing opportunities.
Creativity, Inc. and Creativity Mobile is a creative service provider in the toy industry. They design, develop and produce audio, and also engineer electronic toys, games and apps for all kinds of toy manufacturers and have been part of developing 5,000 toys and learning products. They are always looking for kids to test toys! You can sign up here. They're located in San Carlos.
You've probably heard of Leapfrog and perhaps even own some of their products. You can get on their testing panel, which I believe is in the East Bay (though some testing is done at home or via email). To register for their program, fill out the form here.