Hello Melissa and welcome to JustAnswers,
Very interesting question you have asked today. Went ahead to research what has been reported recently in terms of average household water usage:
1. EPA reports that "The average American family of four uses 400 gallons of water per day."
2. Estimates vary, but each person uses about 80-100 gallons of water per day.
3. As for breakdown by children, no exact numbers as each child and their usage would vary. One report I located shows that
"2 adults/2 children equal 70 gal per day"
I hope the information provided is found helpful as please let me know of any additional questions/concerns you have. Also if you could take a moment to rate my assistance so that I can receive credit for helping you today.