The only place I have stayed at with my kids is Halimar in Haliburton. Fishing for bass, walleye and panfish right off the dock or a short paddle boat trip into the bay. Pool and beach for swimming. Boat rentals too if you changed your mind as well as dock space if you were to bring a boat. They also run a kids camp so you have some you time and sometimes they even overlap so at meals like dinner. The food there is great. We liked it so much we went 3 years in a row. They knew what I liked to 'drink' after the first night and they went to the LCBO and stocked up in-case I wanted a bvg with dinner.
*edit to add* they have some nice bike trails there and a golf course up the road. They even supply bikes to use free so one less thing to pack. If you go just make sure they have bike sizes in working order as I'm sure you can guess they get treated pretty rough from some folks...