Our kids rooms always seem to be a disorganized mess. Their bi-fold closet doors were always off the track and stuff was everywhere. The solutions I have found thus far are:
Buy a really cheap colored flat sheet and hang it on a curtain rod instead of doors. Don't even hem it. I used the sewers tape with an iron to make it the right size! We did this and I LOVE it. The kids can shut the 'doors' easily AND they are pretty darn cute! They also hide the mess!
I also have big wicker baskets (I found them on clearance at big lots) for shoes on the floors of their closets. It makes shoe clean up easy! You could also use a cheap Rubbermaid container for this. Just make sure it's not to deep or then shoes get lost.
I have a friend who used milk crates in their closet. She has two girls who share and a little boy. She put all their fold up clothes in them. You can find them almost anywhere. I found some way cute ones at Wal-mart for around $5 but I'm sure you could watch for sales. They stacked them up with the open end facing out and they all have groves on each side so they will fit together great. I have a dresser and I'm thinking of doing this for toys, shoes and everything else that's in the bottom of the closet!