San Francisco Bay/Marin county with baby and toddler - tips please?

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We have 2 weeks to spend around San Fran in june/july, with a 2 year old and a 6month old. We'd rather not do too much driving and would ideally like to find a beach based rental house to explore from.
Any tips on:

• good beaches not too far north of SF
• family-friendly vacation rental companies
• kid friendly attractions in the area
• anything else??

any advice much appreciated

Bumping for you.

we're off to SF this year. DD will be 5 so a bit older than yours but we will be doing some of the touristy things. DD is excited about the sealions and there is an aquarium at pier 39 as well. Planning to hire bikes and cycle across golden gate bridge. the bike rental company do bikes with seats or trailers for infants/toddlers. The science museum is supposed to be fab but don'y know if it is too old for a 2 year old. Even simple things like cable car rides/boat trips around the bay would be exciting for the toddler.
If you are up to driving a bit, venture to muir woods, north of SF, giant redwoods you can walk inside and a bit a wildlife too.

and if you get up to Santa Rosa you can go to the charles schulz museum and ice rink

Monterey Bay Aquarium -probably a bit far but has an excellent children's section, including interactive stuff for toddlers.

I think SF zoo has just re-opened so might be good now?

Have fun, I love SF!