Free bowling for kids all summer long! Kids registered in the Summer Unplugged program can bowl two games per day, every day, all summer long!" https://
Not into bowling, but interested in more free activities? Try skating: http://kidsskatefree.com
To make up for my forgetfulness, here is another low cost summer activity:
http://www.regmovies.com/Movies/Summer-Movie-Express This link features: "a list of participating locations and start dates. Each location will host the Summer Movie Express on Tuesdays & Wednesdays at 10am for nine weeks. Admission is $1 and a portion of the proceeds will benefit the Will Rogers Institute."
Update: Someone said one of the links wasn't working right. I think I fixed it.