We were looking for a low-key in-house Birthday party idea for our 5yo daughter. We were to have a dozen of kids from 4 to 11yo, so we needed something that would work for all of them. My idea was to make a giant ball pit.
We took out all the furniture from the bedroom, and rented over 5 000 plastic balls. (I wanted to buy them and found a manufacture, but they were sold out)
First of all, it took a while to find a party rental place that had that many balls. Also, we spent about 12 man-hours washing them as they were way too dirty. Anyway...
It was a huge success, and that's what matters. The kids had a ball (pun intended). It was very loud at times, but there were no whining or bored kids! Now the kiddo wants the balls to come back every year. I'm not so sure about that.
[PS: that's only about 2K of balls on that picture.]