There is a Pluto's Pajama Party - however I don't know of GOofy's Slumber party.
Pluto's Pajama Party is around 9:00 or 9:30, the kids can show up in their PJ's (or not) and dance with Pluto, do some activities and songs with him and then they're off to other activities within the club. It's only about 1/2 hour, but the kids LOVED it! They held it twice on our Dream Double Dip 5 day cruise in July, and the kids begged to go back the second time.
Hope that helps!
Oh, and it's for all aged kids in the Oceaneers Club/Lab.