The beach at the Polynesian has signs that it's only for the use of registered guests. I don't beleive I've ever seen such signage at the BC beach, which would be a lot closer for you anyhow.
As others have said, playing on the beach is fine, swimming (or even wading) in the water is not allowed. The state laws require a visible distance to a certain depth before swimming is allowed in any fresh water in the state. None of the bodies of water can meet that requirement.
Anne