My daughter was 4 years old and my son was 1 when we started to look for a new home. She was VERY much into the pink & white stage of life - BARBIES! I hated them. When a realtor would call I would find my daughter in the middle of a tornado mess, with toys all over. It was overwhelming for me and it became too overwhelming for her. She became my "little tornado". I realized that I was giving her so much to play with at one time. I began to limit just what she could play with and packed a lot of it away, taking out something new, every few weeks, just to rotate some of her toys (those that didn't get any kind of interest, were moved out). I provided colored bins to keep it from being a disaster-one color bin for Barbie clothes - another for accessories, etc..... I would also limit the rooms that she could play in, with her toys. She could bring a couple in another room but she had to remove them if she wanted to play with them in the room, again, soon. Let her know the basic rules and reward her if she follows them..."I'll tell you what....if you clean up , every day... you may have a snack after you clean up..." something small. Then you can tell her that she is doing a good job and keep the positive reinforcement going. Little steps.
Same with my husband. He is a wonderful cook but, there are days that he can turn our kitchen up-side down in a very short time. Rather than have the conversation in the heat of the moment, talk to him before the misstep occurs. "Dear....you do this when you cook. Can you please try to keep the kitchen cleaner, maybe loading the dishes while you go along.....etc...." I make sure the dish washer is empty before he even begins. He has gotten better but the habit isn't broken and may never be. However...if I don't "comment" that I appreciate that he has cleaned up the kitchen...I've defeated my purpose. It's what works in my house!
I can't stand going on these rants with my family but I have found that, if I break the problem down in little steps, it's so much easier. Every other week, I still whisk through my kid's rooms and make sure they have stayed pretty organized, removing things that just don't serve a purpose or don't need to be in there. I bring it in my storage room downstairs. If it is not missed for about a month, it goes to Amvets. My kids know I do this (13 & 10) and if it was something that they really wanted to keep, they would have a say-so in keeping it. I just may keep it in the storage room for a little longer or tuck it in the attic if they ever want to "move out" with it. Good luck.