We are moving to the SF area shortly and are looking for a family-friendly place for a long weekend away. Ideally, it would be somewhere within a short driving distance (4 hours or less) with activities for a 4 and 5 1/2 year old. Maybe a resort with pool, etc? All hiking/nature is likely to bore my kids.

Wow, haven't even moved in yet and already you're looking to get away???

Monterey is notable for the Aquarium, and south of Monterey the kids will enjoy the seals at Point Lobos State Park....no matter how bored you might think they will be with nature hikes.
Lake Tahoe is within reach and well worth exploring, I'm sure there is a family resort there that someone else can chime in about.

Lise, for kids your kids age, I would either go to Brockway Springs (Kings Beach) or Northstar. The former has the advantage of being on Lake Tahoe, with a gorgeous view from the pool), it's near a funky town (and the town beach with playground). The condos (not the "highrises") circle a lawn kind of in a horseshoe shape - great place for the kids to play and the parents to hang out.

Northstar is not on the lake but it has a "club" -- health club, swimming pools with snack bar for lunch, etc. It also has ropes things (I don't know what you call them) even for kids (though I'm not sure if as young as yours). It's near enough to the lake that you can easily drive over (15 min. drive). You can stay in older condos, brand new condos, houses, etc. Look on the website.

The condos at Brockway are all older, but they're fine. We used to go there in the summer with a couple of other families, and have been many many times to Northstar in summer and winter. Never ever had a bad time at either (if you discount the time at Brockway that my son came down with chicken pox and we had to leave early!)

HTH

Yeah, I know, Joe .... seems kinda' crazy. I suggested a vacation "at home" exploring all the stuff in SF. But it's been a loooong year already orchestrating this move and hubby would like to plan a real vacation for the end of the summer.

Go to Santa Cruz. Visit the beach boardwalk, swim in the ocean, ride the rides. It's only an hour or so away and feels like a very different place.