Children are not adults, which may seem self-evident but obviously is not. When siblings are assigned to the same task, it’s typical that one or two siblings will do as little as possible while one – usually the oldest – does all the work. That’s human nature, which is fundamentally irresponsible and always looking for the easy way out.
The solution is to rotate tasks among the kids. Picking up the playroom is a good example. The first time it needs to be picked up, assign it to the oldest child. Send the other two kids elsewhere. The second time it needs straightening, assign it to the middle child. The youngest performs the next cleaning, and then it’s back to the oldest.
Voila! The job gets done and no one complains, “It’s not fair!” Or they all complain, which, after all, is only fair.
Then, that evening, send him to bed immediately after dinner. It’s important that you not warn him of this in advance or threaten him with it; simply do it. When he gets over his shock and awe and asks why he has to go to bed so early, tell him that his inability to do the earlier task in a timely fashion tells you he’s not getting enough sleep. So, you’re going to help him with his sleep problem.
Next time the playroom needs picking up, assign it to him again. When he points out that it’s a sibling’s turn, tell him that it is his turn until he does it quickly and properly. When he cries out that it’s not fair, simply say, “I completely agree,” and walk away.
My experience has been that two doses of that will cure the problem.