Sure it can! For example:
Who did you send the letter to?
is grammatical. Some people believe that you cannot end a sentence with "to" because it is a preposition. However, prepositions are perfectly fine for ending sentences with. (see what I did there? =D )
The reason the first sentence is incorrect is because of the "in which" in the middle. "In" implies that they are currently in these situations. But they are not yet in the situation that they are going to be returned to. So it would be correct to say:
The IRS is not concerned with the situations in which these minors live.
Because it refers to the situations they are currently living in. To fix the first sentence but leave the structure the same, I would recommend
The IRS is not concerned with the situations that these minors will be returned to.
As for being idiomatic, I think the first sentence actually sounds better (apart from the "to which" error). The second sentence sounds a little overly formal to me. Although, it's not too bad, and it might just be my dialect.