sounds like you must live pretty close to me (i live in dixon).
depends on ages of kids (if any) and what type of stuff you're looking to do. here's a few suggestions-
jelly belly factory tour (in fairfield)-free, fun, lots of great samples (also the best place to do kid's bday partys),
at christmas time-silveyville christmas tree farm (in dixon)-they have a bon fire, popcorn, hot cider, free 'sleigh ride' (it's actualy pulled by a motorized vehical that has faux reindeer attached)-even if you don't want to buy a live tree it's a neat place to go for a couple of hours.
nut-tree just re-opened in vacaville yesterday. i guess they've put in some small amusement park type rides. if you're into 'big' rides there's 6 flags/marine world in vallejo.
apple hill is a fun place to go to (camino)-if you go to their website they list the different activities each weekend. lots of great food, crafts, some stuff for the kids to do.
fairfield and vacaville both do lots of festivals, activities and such throughout the year-if you go to their convention and visitors bureau websites you can find out whats happening. there's also lots of very good theatre groups in the area, and both the vacaville and fairfield performing arts centers get some excellent professional comics, musicians and such through the year. for more high end stuff there's the opera house in napa as well as copia.
theres no character werehouse at the vacaville outlets right now, but periodicly they open a disney one (seems to be once a year for a few months)-not sure if the folsom outlets has any-napa's def. not.
if you can let me know what kind of activities you are looking for i'll be happy to fill you in (and if you are willing to 'cross the bridge' to contra costa county theres lots of stuff to do).