You could try playing a game with them cause that really worked with me,my brothers and sister.My mother brought us our separate basketball hoop hamper and we would compete on seeing who could put their dirty clothes in the hamper the fastest.You could help them clean it and while cleaning have them find a word that rhymes with their item for example top mop lol and after you all finish cleaning you could take them to a park or something so they could get out their energy after cleaning.I hope this info helps you.
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Break the room up into sections like the dresser, the bed (and what's under it), the book shelf, and the toy box. Say on Saturday morning straighten the book shelf then on Tuesday changes the sheets and pull out all the toys from under the bed etc. Then as each project section completes have them stand back with you and admire their work.