I would like to know: How is this child going to sit in a kindergarten classroom for five hours? I believe he needs medicine but his parents say, "No medication for him." But he's really not normal for his age.
I'm trying to get an appointment for him at the local hospital to see a child psychiatrist. Am I over-reacting? What can be the problem? Do you think he can go to school without sitting down for more than 15 minutes? Is this ADHD?
When kids are "out of control" like this, it's often a signal that some very important need is not being met. At the very least, this little boy is looking for someone to pay attention to him or to set reasonable and consistent limits. If he's been in an environment for a long time that has been too "loose," your nephew may have never really learned how to behave.
You also mentioned that someone said to him: "Daddy is going to hit you." This suggests to me that physical punishment (later in the day?) has been one method of dealing with him. Kids who are hit a lot when they are young learn to hit or talk about violent behavior early in life, for they know no other way to deal with conflict. Parenting (or grandparenting) styles need to be examined, and the family may have to enlist the services of a behavioral psychologist to help them get this situation, and this little boy, under control. Some little children who make a lot of references to sexual and violent themes have been the victims of abuse. Such abuse could have been perpetrated by any number of people in this child's life, and the possibility must be examined.
Your nephew will probably need to be in a very structured and caring preschool for a year or more before even attempting to enter a regular classroom. Without proper intervention, kids like this are often inappropriately labeled early in their school career and this "reputation" can follow a boy for a long time. Keep working on getting that appointment, and get this boy's parents there, too. This is not just the boy's problem. You can also call his school district and ask them for help. Under federal special education laws, the public school has certain responsibilities for kids when they turn three. Educators have experience in matters like this, and may help you get an appointment with the doctor sooner rather than later.