While an adopted child is considered to be your child for tax purposes, you should only enter the number of months the child actually lived with you in the first year of adoption for purposes of calculating credits, etc. Although the child may not qualify to be your "qualifying child" in the first year of adoption, they may still qualify to be claimed as a dependent on your tax return due to being a "qualifying relative." It is possible that you could claim a child as a "qualifying relative" in the first year and as a "qualifying child" in subsequent years.