The best you can do is stay in communication with the mom. And always let him know that he is special.
Hello,
this mother sounds like she really needs some help. Could she be depressed, dealing with too much stress, or have a substance abuse issue?
You are absolutey correct that when a child can not get affection and attention he gets anxious. Many anxious little children exhibit provocative behaviors because they are so desperete to interact with their parents. There is nothing so unhappy as a little child who can not get his parent to interact with him. I sincerely hope you can get your daughter in law some help, because this style of interacting (or not interacting) with a child is sowing the seeds for long term maladjustment. I can imagine that your grandson is a very sad little boy.
Best Wishes
Rebecca Resnik