MY CHILD DOES NOT WANT TO MIX WITH OTHER CHILDREN
Some children have problems with reading other's behaviors and what is expected of them. To make up for that you and your family have made special changes in the way you act and in where you take your child. Over time, without even noticing, your child changed your behavior to make it more limited, predictable, and with few changes. Children, outside of the family, will not even notice that your young one needs such predictability and will bounce around and try to engage your young one, that failing, they will go find someone else to interact with. You may even notice that your young person even turns their back on any children in the vicinity, discouraging any interaction. If this describes your little one, make a list of all your concerns and take it to your pediatrician.
IF YOUR CHILD USED TO HAVE FRIENDS BUT NOW SEEMS ALONE
Speak to him/ her. Find out what the kids at school are like. How they are being treated by those kids? Do they want to even interact with the kids at school? If it is a case of poor fit between your young person and the other kids, try taking him /her to some youth groups at your church, the YMCA, YWCA or Boys and Girls Clubs. See what Parks and Recreation has to offer in the way of activities for that age group.
Some kids have trouble navigating the social world of multiple interactions, and will isolate and become very unhappy during that time. Watch your youngster with others his age and with adults. See and listen to how they react to interactions and what happens as they try to join in conversations. If they seem different and have problems, try to speak with them about it and give them tips. If that does not work, get professional help. Have your child evaluated for mental health issues or need for Social Skills Group.
IF YOUR CHILD SAYS THEY PREFER TO BE ALONE - DON'T BELIEVE IT
It is simply a matter of them feeling like they do not fit anywhere and not wanting to fit in with kids they feel no connection to. They still want a friend. Everyone needs someone they can view as a friend. Isolation is a terrible thing.