Fun break on a less than perfect day. The location outside downtown has a better ambiance since it's open air.
With 2 little kids we had no problem splitting a bucket of sand/rocks between them to pan for gems. The fun lasted about 15 minutes, which is fine for the age of kids (2&4). The find included some fun rocks - they tell you about what you find and try to sell you a polishing and setting of the stone. My kids didn't care about that and the sales lady was kind enough to take our "no" and not push. Don't upgrade to a bucket that guarantees a polished stone unless you're planing to do something with it (i.e set it in jewelry). It's in a baggie in the dirt so it loses a bit of the coolness factor when panning.
All in all, we'd come back again. You can keep all the rocks and my kids enjoyed looking through them for a while after our trip.