I'm having a family trip, in a couple of weeks. We are open to any possibilities but we don't have a car!
You should definitely hike or take a gondala up the skyline-gondola hill which is very easy to walk to from the centre. It's a gorgeous view over the town and surrounding mountains and river, where you can grab lunch, do the famous luge ride and make your way back down on the zip line ecotours. There are also some great jet boat rides on the shotover river which are based at the marina right in the centre. Obviously tons more as well but I can definitely recommend these for family fun and easy access :)