Tax fraud question

I'm coming here for some insight regarding someone I know. This idiot filed someone else's kids on his tax return and now is being audited. He got a letter in the mail about a deficiency. I am not sure how all this works. The mother of those children claimed them on her taxes this year too. He is not even related to those children and has never even lived with them.

Will he be charged? Fined at the least?