for two kids (ages 8 and 5) to clean a bathroom?
Unsupervised, about four hours. With jelly beans as a reward for each completed task, about three. You gain some efficiency on getting the tub scrubbed well if you put the kids in bathing suits and give them buckets. Preps the floor for washing, too!
How long does it take Mom to clean the bathroom after it's 'clean'? Twenty minutes of "Come back and do this part (that you forgot)" plus five minutes to sigh and clean the truly hopeless-to-expect areas.
But if you factor in that Mom got in three hours of work time, it's a pretty good deal.