Ok, so I live in Texas and the step mother of a 3 almost 4 yr old boy, his father and I have sole managing conservator over him, his biological mother hasn't seen him since April 26th, 2009 had has not paid any of the child support on him. We went to court when he was 6 months old. Could we file for child abandonment?

There is a sticky note at the top of this forum that deals with this issue.
https://www.askmehelpdesk.com/family-law/child-abandonment-read-first-364259.html

What you need to define is what you really want to happen here. You don't file for "child abandonment", but it can be used as a means to an end. What is the end you want?