We did this 2 years ago, well 3.5 if you factor in the time my OH had to work for A before moving to the Bay Area
OH is on an L1 visa and I work on my L2 visa with an employment card.
I can only reiterate what everyone else said re the cost of living here. As a family you won't survive on a salary of $120k, that really is very low for this area. Bear in mind that cleaners are paid about $35 per hour and so are nannys can be up to $50 per hour for a good one.
We rent a reasonably nice house in San Jose (they are few and far between) and we pay over $5k a month for that. We then have electric, water and internet costs, which are another $250 - $300 per month.
Then there are car costs. Whilst fuel is cheaper, insurance is more expensive and you will probably lease a car. Depending on what type of car, this will be at least $500 per month, per car including insurance.
Food is another matter. There are 2 of us and we easily spend $800 to $1,000 per month on groceries and toiletries, without the money we spend eating out. There is a real culture here for eating out, but again, it is expensive.
Health care is something else to consider. A have a great package that you would need to join and is taken from your wages monthly. Then you have co pays that are on top and for every visit to a doctor, etc. I had to have some surgery this year and for 2 of us so far we have spent over $10,000 this year out of pocket.
We don't have children, so cannot comment on how expensive after school clubs, etc are, but my friends who have children say everything is very expensive, much more so than in the UK.
Saying all of that, it is an interesting place to live. Within 45 minutes we can be at the beach, 25 minutes and we are driving through the mountains. The weather is lovely a lot of the time. There is no real gun crime unless you live in a dodgy area. Also it's odd as a lot of people, even Americans, moved here for work, so don't have family close by.
A couple of final points - 1. Don't underestimate the costs, everything here really is crazy expensive ! 2. Remember to factor in the cost of trips home. 3. Don't underestimate the time difference and the loneliness you will feel for the first year or so.
Feel free to PM me if you have any questions.