As Wildh2onriver said, Ruby Horsethief is pretty mellow, but at these flows, a five-year-old in the water could be a really bad situation. As an experienced taker of young kids on river trips, I can say that you will need a good, properly fitting pfd for the little one and a spare "kid wrangler" on board with the little ones at all times. In camp, little kids are like magnets to the water. They will need very close supervision during the entire time and should always have their pfd on when they are anywhere near the river. At these flows, a kid who wades too far in or falls in the river from camp will be swept away very quickly.
Magnets may be an understatement, as soon as you look away, they head straight down to the water, and they love to walk right up to cut banks and ledges, oblivious to the danger of falling in.
I am not saying not to go, just keep a laser eye on those kids and put them on the safest boat and have a kid holder/wrangler with them.