The son looked NOTHING like the mom

He's mixed, Obama probably didn't look like his mom.

If you take time and look into the real story you will learn that Carla had him at a young age. I don’t remember how old but maybe 16 or 17. She had left home I think due to her father or step father. She became involved with an older man and had her son. I can’t remember if they were married or not. I can’t remember why they separated. The real Carla had three sons and one daughter. Also were victims of this entity not just her.

http://www.ghosttheory.com/2009/05/18/the-entity-interview-with-doris-bithers-son/comment-page-2#comments

The actor who played her son (David Labiosa) is 13 years younger than Barbara Hershey and he was 21 years old during the making of the film. It's stated in the film that Carla was pregnant with him when she was 16. Technically if the actor was 3 or 4 years younger he'd have matched up perfectly age wise. It's not too big a discrepancy, certainly forgivable.

As for the physical appearance, people of mixed racial backgrounds can looks drastically different from their parents. It's not outside the realm of possibility for a Hispanic father (with notable Native American admixture) and White mother to have a son look visibly Hispanic.

His father was obviously Herb Sanchez.