Abandonment, New Mexico, Husband deployed?

My husband is currently deployed til sept of 2011. His ex wife has abandoned their son with her uncle, the uncle contacted us to take the son, but we want to do everything legally! We live in TX but the uncle, son, and ex wife are in NM. My husband and his ex wife got divorced in NM, in the divorce my husband has visitation rights, even though his ex wife will not let him see his son because he got married to me. The uncle has told us, the ex wife is on drugs, and abuses the son. What can we do to get custody over him so he is in a safe environment? Or what can I do to get things rolling for my husband when he gets back?