Squall knew this was coming but was still really overwhelmed by all of it. As the description implies, he's never really had a birthday party so he's just really happy with all of this and really appreciates his friend.
Stan was also present. He helped with whatever was needed for set up and just made sure things ran smoothly so everyone could have fun.
Robin might have come to meet other teens if that was cool. But maybe not. Depends on Steve and Nancy.