North Stradbroke Island 

Cylinder Beach - surf beach but often has a safe sheltered lagoon for the younger kids.  There is a good playground on the foreshore with toilets, showers and a laundry.  There are bbq's, shelters and shade trees.  A campground is located adjacent to the beach.  The Straddie Hotel is located to the left of the beach, (take the stairs up and follow the path) it offers a great outdoor deck area with magic views.
Brown Lake, located just off the Trans Island Way. A freshwater lake perfect for toddlers with shallow, smooth waters.  There is a small playground, picnic tables and toilets.