Why on earth do they do this?

I have been pondering this question since Dylan's birthday party, in November, and I have yet to come up with a good answer.

I love my nephews so much, but every time they come over, they dump toys out in Dylan's room. In all fairness (in case my sisters are reading), Dylan joins in on the fun. He only does this with his cousins, though. This doesn't happen when other kids come over, and Dylan never does it on his own. Perhaps it is the fact that a 5 year old, 4 year old, almost 4 year old, and 3 1/2 year old are all involved...and that they are all boys?

When I say dump out toys, what I mean is TRASH THE ROOM. I always think I should take a picture, because I don't think people believe me when I say how bad it is. But when I see the mess, I try to walk away as fast as I possibly can, and I don't think a picture could even do the mass destruction justice.

The first incident occurred at Dylan's birthday party. I spent 2 days cleaning up the mess in his room after that one. The worst incident was just a few weeks ago, during family game night. Dylan's room was so trashed, that I had to kick toys into his room, that were spilling out into the hallway, and shut the door before heading to bed. Dylan slept in our bed, because I couldn't even walk to his bed. I should have put police tape over the door, with an "Enter at your own risk" sign.

The next morning, I started to go through the mess. The boys had even dumped out dresser drawers, ripped the bedding off the bed, took the shoe organizer off the closet door, and dumped those contents into the mess on the floor. It took me 5 hours to clean Dylan's room, and I ended up throwing out several broken toys.

So...I learned from that. Or so I thought. For Lexie's birthday party last week, I moved about half of Dylan's toys into my bedroom. I figured that would minimize the mess. Everything with little pieces or lots of pieces got put away. After the party, my two brother in laws and I attacked the mess in the room, and it took the 3 of us over an hour to get it cleaned up. It took me an additional 2 hours the next day to clean, and once again, I ended up pitching broken toys.

This weekend, they came over again. I took out 80% of Dylan's toys and put them in our room. His room was so empty that when you were in it, your voice echoed. I thought that would do the trick. Nope, it took 3 hours of cleaning, and I threw away more broken toys. Somehow the toys made their way into every room of our house, as well.

I'm at a loss of what to do.

I'm thinking I need to empty Dylan's room completely, and just replace everything with an inflatable bounce house. I doubt that would even do the trick.