Forget about Whistler. Maybe in the Winter.
The Wedgewood is great, steps to Robson St.
The Westin Bayshore (
http://www.westinbayshore.com/) appears to have a special summer rate. The Bayshore is next to the seawall that circumnavigates Stanley Park, home of the Aquarium, as well as many trails to bicycle/walk. The Bayshore is a 5 min walk from Robson ST. Rooms with nice water views, next to a large marina.
The Capilano suspension bridge is quite expensive for a family, The suspension bridge in Lynn Canyon is free, almost as exciting.