Clearly I have limited experience with child ownership (oh, you don't own them?), but I have a lot of opinions...A.LOT.
Not very recently I attended a birthday party for a child a friend of mine owns (get over it). The party itself was quite nice...lots of booze, good food, adult conversation...I almost forgot I was at a kid's party. It was a couple of hours into the party before I realized I had seen no more than 3ish children...it took me awhile because it's my natural state to be surrounded solely by booze and adults.
I commented on this to the friend with which I was in conversation (and who had 2 kids at the party). Turns out there was a Bouncy Castle!!
Admittedly I am the first person in line to judge parents for spending more than 20 bucks on a 1 year old's birthday party (seriously people, they are not going to remember it...shove their face in a cake, take a few pictures to show them when they're 10, and you're covered).
But truly I must rescind all previous judgments on the toddler party circuit...I.LOVE.BOUNCY.CASTLES. They are crack for kids...$200 well spent. Kids are strangely compelled to spend all their time within the Bouncy Castle, only to come out for cake or frenzied gift opening, and then immediately return so the adults can continue boozing and telling themselves all's well with the world.
Perhaps that is not the same reason parents love them, but I will now go to any kid's birthday party where there is booze, food, and a bouncy castle.