Abandoned children found with skeletal remains of sibling in Texas…

I don't understand what happened to the parents. How were they questioned and released without charges being filed I wonder?
 
I don't understand what happened to the parents. How were they questioned and released without charges being filed I wonder?

The kid has been dead for over a year and the parents (mom and boyfriend) haven’t lived there in several months. How have they not been charged with at least child endangerment????