I recently ran across a news story that illustrates why we need strong boundaries when caring for traumatized children. A teacher found herself sentenced to jail after a jury acquitted her of a sexual relationship with a student, but convicted her of pursuing an illicit relationship. The verdict may be a compromise among the jurors, but it's instructive to look at the evidence that the jury heard.
According to coverage of the trial, the student claimed that the teacher had initiated a relationship with him that turned sexual. The teacher claimed that she never had any sexual activity, but that she established a relationship to try to help him. She and her husband let him move into their home and took him with the family on vacations. She also bought him expensive gifts, including a firearm. The arrangement appears to have been informal, with no official foster care placement or guardianship transfer.
The relationship may have been innocent throughout, or it may have been sexual at some point. From the outside, though, the lesson is to follow very clear boundaries when trying to help children. First, never accept a child into your family without some sort of official court order or foster care placement. You need that objective oversight (as annoying as it can be) to provide accountability and some degree of protection. Second, the teacher's daughter testified to aggression and violence from the alleged victim while he was living with them. If a relationship turns chaotic, don't put your family at risk while trying to help the at-risk child. Sending him home may be emotionally difficult, but hindsight makes clear in this case that it would have been the most healthy choice for the entire family.
Finally, follow boundaries to protect yourself from allegations. Don't do things that can be characterized as grooming (in this case, expensive presents). If you worry that a child may claim abuse, limit the times that you are alone with him or her. Helping children is admirable, but be careful not to put your entire family at risk while taking care of someone else's child.