what happen at the end?

"Mitchell" lures Jonathan outside, terrorizing him as usual. The mom comes out and Mitchell is going nuts, holding Jonathan hostage and threatening to throw him into the lake. He tells the mom she needs to choose between him and Jonathan. The mom yells, "Give me my son" (I think this indicates that she realizes "Mitchell" is not really her son). He jumps into the lake with Jonathan, who can't swim. The mom jumps in and rescues Jonathan.

The next scene is the mom and dad sitting in Mitchell's room, which has been boxed up. The mom has received the DNA results from the lab (from the hair sample she took). She decides not to open the envelope. The dad says they can drag the lake again to look for Mitchell's body and asks her what she wants to do and she says she wants to let Mitchell go.

The final scene shows "Mitchell" hitch hiking along the highway.

Thanks