Parksville / Qualicum Beach is one of the best flying day-trips from Greater Vancouver or Victoria.
Besides offering what is probably the nicest beach in British Columbia, there are lots of other family attractions, decent hotels, and reasonable restaurants. There is even a great restaurant right on the field.
It's a $15 taxi ride to the beach - go to the one in Parksville (ask for the "Beach Club" entrance).
The best beach is actually in Parksville - not QUalicum Beach proper. But it's a short taxi-ride, and well worth it. Try and time it for low tide if you can.