If you live in (or are visiting) south-central Pennsylvania and enjoy state parks, I would recommend visiting Codorus State Park. There are hiking trails, boating, and a very small beach that families can enjoy together. The big draw, however, are the two disc golf courses. One is more in the open, while the other one is more in the trees. Both are a lot of fun to play.
There is also family camping, and some of the sites do allow pets. There is also walk-in camping that is more primitive. We haven't tried those out yet - we're waiting for the little one to get older!
If you've never tried disc golf and are visiting the area, I would recommend stopping at Codorus. It's a blast! Be sure to bring your frisbees!