My lovely but disorganised DS (nearly 7) has his own room with boxes for lego and playmobil and the deal is that I have to be able to come in and chat without killing myself on toys from Sat to Friday.
On Friday, we have the Frid'y, Tidy when everyone mucks in a bit more to get the house done for the weekend and I hoover his room a while after he comes in from school.
The deal is that if it is chaos he has to do it himself. If it isn't too bad he gets help.
He has got into the swing of puttng a bit of shape on it from Thursday onwards.
He did try shoving everything under his wardrobe this morning though. Worth a try,I suppose.
DD2 is naturally tidy at 15 months: today the pencils on the floor were annoying here while I was reading so she got down, picked them up and put them in the pencil box before coming back for the rest of the story.
DD1 is 3.5 and does fine if her tidying is structured (so, I ask her to pick up the toy people, then the toy food etc).
We have a tidying up song (Tidy up the carpet,tidy up the floor / Tidy up 'til we can tidy no more' and when things get out of hand we do a two-minute tidy and everyone has to put away an age-related number of things.
Everything has a place to go and lego and playmobil are only played with in one room so that helps too.
We also make a huge fuss about anyone who recovers a missing bit, or old favourite, as we go.
This over-regimented set of tactics has pretty much got rid of the bin-bag threatening style of tidying we've had in the past.
I really don't mind the mess buidng up unless the floor gets unsafe to walk on or people are getting upset about missing bits ...