There are a number of beaches literally just across the street from some of the residential neighborhoods as I recall. I do believe that our "guide" on a city tour we took said something about rather chilly water temps not much above 50 degrees FH, even in the summer.
I don't know the ages of your kids, but, check out things like Stanley Park and the Vancouver Aquarium. Catalano suspension bridge and the treetops trail. Grouse Mountain Tram. Take the family on a day trip up to Whistler, check out the Village, and their are many places to stop and check out on the ride there and back.
Perhaps a side trip to Victoria and while there a whale watching excursion to see the Orcas out near the San Juan Islands.
There are a few nices beaches to visit while in Vancouver. In downtown Vancouver the best beach is English Bay Beach. Outside of downtown Vancouverites/residents spend most of the time on Kitsilano Beach, Spanish Banks & Jerico Beach. Enjoy the sunsets!