This weekend, September 10th and 11th is the Brandywine Festival of the Arts in Wilmington. For $5.00 you can get admission for both Saturday and Sunday as well as admission into the Brandywine Zoo.
I went last year and it was really nice, but just so that you are aware, IT IS AN ART FESTIVAL, so most of the vendors are artsy related, Including my Mother, who will be there selling her beautiful jewelry. Look for Turquoise to Pearls when you are walking around.
Parking is the most tricky part of the whole festival. I recommend parking at one of the shuttle locations and bus yourself in. I did it with a stroller last year, and it was fine.
Check out the website for more information and a list of all of the vendors as well.