Parents of one kid in diapers spends around $60.00 to $100.00 per month in diapers so that would equal to $720.00 to $1,200.00 per year for disposable diapers per kid.
If the kid wore diapers until 3 years old you'd spend $2,160.00 to $3,600.00 per kid on disposable diapers.
Disposable diapers are costly over the long run and it's usually cheaper to cloth diaper and you could put that money that you'd spend on disposable diapers into a savings account and it could buy your child a car when they get old enough to drive.