For summer I recommend bike riding at the park- that's a lot of fun.
Another thing is to maybe push the furniture out of the way- put on some music and dance! Get some kids songs CD's and jam out with the kids
Or even some games on the wii- they have some workout ones that you and the kids can do together i'm sure. Even dance dance revolution might be a good one for the 7 year old (not sure about the 5 year old).