Would like to know WHEN a child can decide for his/herself on where they want to live.. With the grades failing, as the lack of concern at the "primary residential custodians" house. Giving Nyquil to sleep, not for a cold, just to get them to go to sleep. My son has a "heart condition" and NOT to be taking any kind of expectorant and she continues to give it to him knowing what could possibly happen. Please help!

Kids don't get to decide for themselves. A judge will decide what is best for them based on many factors. If they are older, say 12-16 or so, I'm sure that he will ask their opinions and what their reasons are, but ultimately it is his decision. Have your ducks in a row with facts (ie Dr's notes) and proof of what you are going to present at the custody hearing. It sounds like you need to schedule another hearing.

They can decide where they want to live at at 18 years of age.

In Tennessee normally the judge allows them to talk in court as to what they would like, but that does not hold all the weight.

To move custody, the non custody parent will have to file a motion in court to modify the court order to give them custody.
You would need to PROVE what you are claiming with evidence the court will accept

Please pay more attention to posting guidelines. There is a Read First sticky in the Children forum (where this was moved from) that directs questions of a legal nature to this forum.

Had you done so you would have found many threads addressing this issue with the answer.

If you want to change custody file in family court for a modification.