Oh man, this place is fantastic! It's loaded with excellent activities for kids of all ages including a rotating summer showcase (last summer the them was Mr. Potato Head and this summer we've got Tinker Toys). The hours are flexible, free parking is available, staff are helpful. The facilities are clean and highly accessible with strollers, etc.
I love taking my son here to explore for a couple hrs. Best part is that it's free! Imaginon also has several theaters for kids to enjoy a variety of shows (occasionally free as well, but usually a low cost ticket purchased in advance is required).
Don't forget to check out the used book sale on the first floor - everything's less than a dollar and proceeds benefit the Meck. County library system.