The Chabot Space and Science Center is located in the hills of Oakland, CA. It's full of many great exhibits and even has a planetarium. There are several shows in the planetarium including laser shows and shows about how the stars move across the night sky.
The exhibits rotate often and there is a kids area that has numerous activites that are geared for children. There are even maps and coloring books you can check out for your kids and activites that require them to get stamps.
Admission is about $10 and depends on the activites you want to do (e.g. it costs more if you want to visit the planetarium and see a couple of shows)
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