How do you prove someone to be an unfit parent? What would the court want to see? What if it's not a phyiscal abuse but mental; where every time the child sees the visiting parent after a few months each time the child returns with tears, very odd questions and concerns, and completely different from his/her usually character after seeing the visiting parent. Is that some type of abuse/problem? Is that characteristics of an "unfit parent?" If not then what is?

The definition of an unfit parent is governed by state laws, which vary by state. A parent may be deemed unfit if they have been abusive, neglected, or failed to provide proper care for the child. A parent with a mental disturbance or addiction to drugs or alcohol may also be found to be an unfit parent. Failure to visit, provide support, or incarceration are other examples of grounds for being found unfit.

Consult family lawyer for specific requirements in your area.