If you only have one day in Vancouver, here's what I'd do: 

• Park at Science World (flat rate $12 until 6:30 p.m.)
• Science World admission is FREE with Pacific Science Center membership and it is super fun
• Take the Aquabus from Science World to Granville Island
• Granville Island! There's a 2-story kids market, artist studios, a public market
• Take the Aquabus back to Science World
• IF you still have time, walk over to Chinatown