We were able to drop our toddler off at Small World Nursery before we ran the 5K. For the older kids, on-ship youth activities aren't listed open during the day (according to the Navigator I have in front of me, they were open 4:30-midnight on CC day). That being said, on the insert, the Oceaneer Club has an open house starting at 9:30. What I'd do is stop by at some point early in the trip and ask what sort of arrangements can be made. With the 5K being ages 12+, I'm sure there's some sort of arrangement for kids to have a place to go while their parents run.