The entire time. We have actually yet to take our kids, but everyone we go with that has kids, take them.....and the kids wear vests all the time.
Well, not while eating and the like.... But when people are just having fun, the kids have PFD's on....even the older kids. If they were them in the normal boat, they wear them on the houseboat.
Better safe than sorry.... Seems like too often you read about a kid drowning at Powell after falling off a houseboat.