What is the criteria for a "qualifying child"

"The easiest way to figure out who may claim a dependent is to enter information in TurboTax, and the program will determine if you can claim the children".

Your Two possibilities to claim a dependent are as follows:

You may be able to claim your [son/daughter] as a Qualifying Child dependent if:

1. The child must be related to you. The child can be your son, daughter, stepchild, eligible foster child, brother, sister, half-brother, half-sister, stepbrother, stepsister, adopted child or an offspring of any of them.
2. Your child must be under age 19 or, if a full-time student, under age 24. There is no age limit if your child is permanently and totally disabled.
3. Your child must live with you for more than half the year, but several exceptions apply (i.e., away at school).
4. The child cannot provide more than half of his/her support.
5. You must be the only person claiming the child
6. The child must be a US citizen, resident alien, national, or resident of Mexico or Canada.
7. The child cannot file a joint return with his or her spouse.

 

You may be able to claim your [son/daughter] as a Qualifying Relative dependent if:

1. You provided more than half of his/her support in 2016
2. He/She earned less than $4,050 in gross taxable income. (Social Security income generally doesn’t count here.)
3. He/She lives with you 365 days in the year or is related to you.
4. He/She isn’t a dependent on someone else’s tax return.
5. He/She isn’t filing a tax return with a spouse (married filing jointly).
6. He/She is a U.S. citizen, resident alien, national, or a Canadian or Mexican resident

You can’t claim a dependent if you are a dependent on someone else’s taxes

See Rules For Claiming Dependents