For all three income-driven repayment plans, your family size includes your children if they receive more than
half of their support from you. You may count your child when determining your family size if you provide
more than half of the child’s financial support, regardless of who claims the child for tax purposes or who has
physical custody. If you do not provide more than one-half of your child’s support, you may not include the
child in your family size for income-driven repayment plan purposes.

For more information go to the Income-Driven Repayment Plans: Frequently Asked Questions Website