We've had several boys in our home and some have been messy and some have been neat. We are foster parents and have had 8 kids in our home since 2003.
We've had several kids "hoard" things. By hoarding, I mean they hide food, things under their bed or under other furniture. With our kiddos, they put everything underneath their bed, food, clothes, toys,etc.. This may be the start of hoarding. No, that doesn't sound typical to me. I have a 2 year old and he is messy too, however I encourage him to clean up and usually he does clean up.
Have you tried doing a reward system? You could get a chart at Mardel's or a school supply store, even Wal-Mart or you could make one. You could put his chores or have the cleaning up on there and put each day on there. Each day track him and rate him on it. If he picks up his trash, then he gets a star or check mark. You could reward him then and let him stay up later or read an extra book,etc.. Or you could wait and do it at the end of the week and see if that works better and do a bigger reward like a renting a movie or getting extra books at the library. I would try this and see if that helps at all.
If that doesn't work, has there been any major changes in your home lately? Does he go to Pre-K or a sitter? If he does, is there any changes there? I would talk to the sitters or teachers, if he goes somewhere like that. It could be his way of dealing with his anger or he's frustrated.
Most of the hoarders we have had have been extreme cases. One child was homeless and that was his way of keeping his things protected and safe by keeping them under the bed. He may have had to do that in the shelters that he lived in, as a way of keeping his things out of the way. Usually they may feel threatened in some way.
It was frustrating cause I kept finding things under everything in his room. What we did, and this is like a last resort for you is to get play therapy. Play Therapists are wonderful. They have ones that can come to your home and then there are play therapists that work out of their offices. They all have different styles. You can actually play with your child on the floor and do this consistently and you learn a lot. Children's play is their work and that's how they communicate is thru their play. If you have some cars or something where you can do other things with it, you might try playing cars with him. Drawing and art is a good outlet too. You might want to encourage him to get outside and play for at least a little while or do some type of activity that maybe he can do by himself. Maybe he needs some more one on one time with you. You might try spending a little extra time with him before he goes to bed, however after your other child goes to bed.
Is there any food issues? If it is mostly food under the bed, that could be part of it. Do you have any animals, do you think he is trying to hide it from your dog/cat?
What I did, was I checked under the bed every day. We had other issues going on, so we had to focus on several things.
We use Love and Logic and lot of schools use that too. Check out their website and you may want to read the book or get a video from them. It is www.loveandlogic.com
Hope this helps, C.