Do these tasks during

Your children need to learn how to organize, how to work efficiently, and how to stick to a task. You will probably have to do this work with them for awhile until they have learned how. After you feel they have successfully learned how to do the work, you will then need to inspect it after they are done and hold them accountable. If they see you doing these same tasks in your bedroom while they are working, they will work more willingly. They hate to feel that they are missing out on something else that is going on in the house

Week 1

Have the children straighten and de-clutter the tops of their
desks
dressers
tables
window sills
or any other flat surfaces in their bedrooms. Assign one surface per day, or assign a time period per day, or assign a day of the week to spend some time on this area of their bedroom.

Week 2

This week have the children clean
under the beds
After shoveling it all out (the fun part) they might be overwhelmed.
Give them a trash bag for the trash.
Then put all books away.
Next, all stuffed animals,
and the rest of the toys.
Finally, whatever else is left. Hopefully, there are no rotten apple cores.
Like everything else, if this is done on a regular basis, it never gets that bad. But left for 6 months, it can be quite a trial.

Week 3

This week is for the children to straighten their closets.
Have them get in the corners, nooks, and crannies, and dig all the things out that they might have tossed in and forgotten about.
After digging out, they must put things in their proper place.
Put the clothes on the shelves or hang up. If they are old enough to sort out the torn, stained, too small, unworn clothes have them do so and put into the trash or a give-away box.

Week 4

This week, the children de-clutter, straighten, and thoroughly dust the shelves in their rooms.

Week 5

This week have the children clean
windows, as needed and if able to,
walls, de-clutter and catch cobwebs,
light switches, wipe grime from,
lights, dust and change bulbs if able to,
door, dust top, wipe grime and door knob.