How close are you to Gurnee? If close enough that you feel they can drive there, they can work at Six Flags. I did that in high school and it was fun. Or a mall, grocery store, or fast food restuarant. They can also babysit, do odd jobs for neighbors or the elderly.
Call 311 for information on the Mayor's summer work program. Check out neighborhood community centers (YMCA and JCC both have centers all over the city) and park districts; there must be day camps around that hire teens. Advertise at the grocery store; people in your neighborhood are probably looking for teens to do odd jobs, be a mother's helper, etc. The high school that your kids attend will also have resources for summer employment.