Ahoy, Joy!
You will be happy to learn that
Scuttle's Cove is indeed open for you in time to check your little cruisers into the club before you start the Castaway Cay 5K. You will need to go to the lounge where the 5K check-in is that morning, check in and get your race bib, and then let the Cast Member in charge know that you will be making the stop to drop off your kiddos.
The minimum age to participate in the Castaway Cay 5K is ten years old. This was exciting news for my daughter, who is eleven, since the minimum age used to be twelve. We are booked on a "double dip" to Castaway Cay this July, and our family plans to participate in the CC5K on both of our days there. We can't wait! The new medal for 2015 is awesome!
The Castaway Cay 5K is something that we try to participate in on every cruise. Over the years, we have seen this informal race grow into an actual race, complete with a runDisney medal. The path that you run is nice, although it is always hot and humid. Be sure to drink water as often as you see the stop. This is not an officially timed race, so take your time and do a little sightseeing while you are running (or walking).
I hope this helps with your cruise planning. Please let us know if you have any more questions that arise as your cruise gets closer.
Happy Cruising, Tracy V.