What kind of things do you guys want to see? Our family is going to try the TMZ tour but my kids are older and they watch TMZ with me every day so they know what they're in for. There are Greyline tours but I haven't heard many good things about them. I've heard the movie star homes tours are the worst. You see mostly gates and bushes. A hop on hop off might be ok because then you can just do the stuff you really want.
I think you can probably do pretty good on your own if you have a list of things you want to do and see.
Some examples are
Hollywood and Highland/Grauman's Chinese theatre/Hollywood Walk of Fame/El Capitain/Disney Soda Shop These things are all in the same area so you hop off here and explore.
The Grove -Sometimes celebrities shop and eat here. They film Extra here too so maybe if you're lucky you will see someone famous.
Rodeo Drive/Sprinkles cupcakes. Lots of people like to get a pic on Rodeo drive just to say they've been there. You can check out the only cupcake ATM in the world at Sprinkles while you're in the neighbourhood.
The hop on hop off goes to lots of other places too. Santa Monica etc
http://www.starlinetours.com/los-angeles-tour-HOHO.asp
If you meant like a studio tour you can always do the Universal tour with kids of any age. Paramount they have to be at least 12. I know someone who did the Paramount tour and they thought it was great.
Something fun to do and see a real studio might be to see a taping of a real show. Tickets are free and there are a few Disney shows you can see. It makes for a long day though. You have to be there a couple hours early and the taping itself takes a couple hours.