Hi there... how long is your nap? I am assuming an hour or so?
The kids could go to the pool and swim, they could go see the animals at the arusha lookout and talk to the guides who are stationed out there.
There is a hidden mickey safari they could do - it is a sheet of clues to find all the hidden mickeys in the hotel.
There is a daily tour - but this could be boring for kids their age - I think it's at 3:00pm.
They could go to the arcade, or grab a snack at Mara (the food court)
If the 15 year old is responsible enough - the bus ride is only 5 minutes or so to Blizzard Beach or Winterland/Summerland Mini Putt - they could go do that.
My bet is they will hang out at the pool - I can't imagine kids gettin tired of that it is such a neat area.
Have fun on your holiday.
>>^..^<<