Can I claim as a dependent relative an adult child got stimulus checks?

An adult child of mine received the first two stimulus checks. Now, in 2021, I can see that it makes sense for me to claim the child as a dependent relative. The child passes all of the tests to be a dependent relative, and I think that would allow me to write off the  substantial cost of residential treatment they underwent in 2020. 

Does the fact that the adult child cashed the checks preclude me from claiming him/her as a dependent relative? 

Would my claiming this person have other consequences - would the stimulus money have to be repaid to the government?

Thank you for your help!