Yep, it's a "free" park. All ages, I was 4-5 the last time I went and my little brother was 2-3. I was looking at their site and it seems like that have WAY more stuff (and nicer!) than when I was there.
It's kind of a like a small town carnival on crack - plenty of kiddy rides with a good mix of thrill rides. Be sure to get the coupons off of Holsom bread ($4 off all day hand stamp).