That would be a good time to visit Green Bay. I am not sure of the Packers practice schedule but it should be happening around that time. 
Bay Beach amusement park would be a good stop for your 11 year old. There is a nice railroad museum in Green Bay also.

In Manitowoc the Maritime Museum with a submarine is worth a visit. The Cedar Crest ice cream factory store is worth a visit. 

There is plenty of parking for the Brewers. It is a little bit of a walk but not bad. 
The Wisconsin State fair is in Milwaukee from July 31 to Aug 10 if you are interested and can make that work. 

That is just some thoughts for you. 

Chuck