Hi dieguy, Welcome to LSCN.
We too have little ones. Our son, David, is 8 and our daughter, Erin , is 5. Strawberry island is great as well as out in front of Mac 'n Rays. We have also stopped and played at the sand bar as well as at Gull. If you go to Gull, you have to judge the crowd yourself as it can vary from families with kids to those who have lost all common sense. As long as you dont hit Gull on an organized weekend, it is a fair shot. The other place we like to go is on the south channel side of Seaway Island. Nice beach, good campfires, kids love watching the freighters go by so close (make sure you have a good anchor as water levels can vary by as much as 3' when they pass) and then they do a little surfing as the water rushes back in. Just remember you are on Canadian soil and techincally need all the proper papers, yet we have not been bothered in all the trips we have taken.
Where do you keep your boat? Be nice to hook up on the water and introduce the kids to each other. Not to mention the adults as well.