While it's great to get outside and play in the summertime, sometime kids (and parents) need a little down time. A great way to get out of the heat and still have fun is to see a movie. Some local theaters around the Bay Area offer free summer movies, or very low cost movies.
Regal Theaters have many locations and off free G and PG second run movies on Tuesday and Wednesdays. To see if there is a participating theater near you, you can visit their Free Family Film Festival schedule web-page. Not all Regal theaters are participating this year, including some that have participated in the past.
AMC Theaters have a similar program with movies for $1.00. For their list of participating theaters and the movies they will be showing, their Summer MovieCamp website is here.
Cinemark (Century Theaters) also have $1.00 movies for kids this summer. If you plan to attend most of the shows, they also offer a prepaid 10 week Summer Movie Clubhouse card for $5.00.