I was just there yesterday for our friends' 1 and 3 year olds' birthdays. Adults aren't counted, but can jump (bring socks!). First in one room for some period, then into another room with different jumpers and giant slides. Everyone who enters has to have a waiver... so yeah, my five month old was cleared to "participate" lol, but wasn't part of the head count.
I thought the staff were friendly and helpful, but the rap music that was playing at first was too much. I'm not sure if someone from our party mentioned it to the staff, but about 15 minutes before we left (when we were in the room for food and gifts), it was changed to a country station. Just seemed like they could have had on Radio Disney or something that was actually geared toward kids. Aside from that, it was a lot of fun. Between children and adults, there were probsably 45 or so people in our party. It never felt crowded. We were a little rushed at the end, but the birthday kids were late, which probably accounted for that.