He had dark urine, then perhaps something was already too far gone to handle it. I think they were trying to counter kidney problems, maybe wanted to avoid doctor. But sadly, should not have!
If the kid had continual dark urine, it might have been a liver problem, not a condition of getting too little water and not solved by drinking vast amounts of water in a short time.
Even if the dark urine was due to dehydration - drinking too little water, the solution was not to have the kid drink an adult male’s suggested daily amount of water in just four hours.
Sometimes parents go to doctors too little. Sometimes they fail to consult doctors often enough. And parents should not think that “solutions” that seem “right” for an adult are appropriate for a child.