I see from your profile you are in Virginia.
So a place like the Smithsonian in Washington DC may be good. Some museums have special activity days where children can do fun experiments and learn about various sciences.
Also maybe have a word with the Children's Librarian at your local library. Most libraries have summer reading plans and also activities. At my local library this summer I know there will be presenters coming in from the National Parks service to talk about wildlife and a lecturer from the local State University to talk on astronomy. You library may have a similar program. If they don't maybe you could suggest that they do provide one.