Absolutely. Check the crime stats on San Mateo, here:
Basically anything Green, Orange, or Purple is okay. Yellow, especially East of 101 is very much not okay. Blue is marginal, gets better as you get closer to Belmont.
A good rule of thumb when looking at San Mateo, Belmont, and San Carlos is that as you go West from HWY 101 and up into the hills, things get better. The narrow strip between 101 and El Camino Real is usually "lower end" and things get progressively nicer as you move West of El Camino Real.
I know these areas very well and have been shopping for homes there for almost two years. I'm not a realtor, just a buyer with a young family, just like you.
Also check out http://www.redfin.com,
which has free access to the MLS data, plus demographics, trends, school ratings, etc., etc. Note that if you use Redfin to buy a house, they'll rebate 1.5% of the buyers agent commission to you in cash (you can use it for closing costs or just take a check). They also have great forums with a lot of very helpful posts and NO realtor ads. Sometimes on Trulia you don't actually get any info, just 100 Realtors saying "best to have an agent, call me dearie".
Good luck and let me know if you have more questions about San Mateo / Belmont area. Sorry, can't speak to Mountain View.