L.S.
Both my kids are summer birthdays, so we've stuck to indoor parties and have had Gymboree and Little Gym. For a 4 year old, I would recommend Little Gym. The kids had a great time and it was so easy on the parents. The first thing they did was sit in a big circle, introduce themselves and show off their best gymnastics move in the middle. There was a somewhat organized inflatable activity and zip line and a lot of free time tumbling. Seems like they did some games with them also.