I had foster kids for 11 months and i paid tuition out of pocket in 2017. I have paperwork to back this fact. What happens if a bio parent claims them as well?

[LindseyLO]

If you have the right to claim a dependent claimed by someone else, then you must print and mail your return if you are not the first one that files. The first one that files with your child will be able to e-file.  The second return will be rejected and must be mailed in.

• The IRS will process your return and pay your refund if you are entitled to one.
• Later, they will contact you and the other taxpayer to determine who is entitled to claim the dependent. (The IRS is not allowed to tell you the identity of the other filer.)
• The taxpayer who incorrectly claimed the dependent will be assessed any additional taxes and penalties, and required to file an amended return

Here's the info on how to file

https://ttlc.intuit.com/replies/5621529