I have a neighbor who has two children. They live with a man they call dad but is not their dad. The children's mother is never home with them. What is the law regarding abandonment? How long of an absence constitutes abandonment and if that is found could a noncustodial,non biological care giver allowed to geain custody?

Abandonment is a criminal charge involving leaving children without adult supervision. If the man is there, then its not abandonment.

Even if the mother leaves the children with this man for months at a time, its none of your business, unless you have proof the children are being mistreated.

And as a non relative, you would have a very slim chance of getting custody of these children.

May I ask why you are sticking your nose in this?