Tips for discussing your concerns
When approaching the subject with your child you could try and discuss your concerns subtly. Perhaps query which relationships they value at school, who they spend their time with and if there are any children that they don't like.
If your concerns are warranted and you find out your child is experiencing difficulties with their peers the most important thing you can do is let them know that you will help and support them.
Try to put your own feelings aside and reassure them that it's not their fault and that you love them. In some instances, children feel better about talking to an adult that is not part of their immediate family. Therefore referring them to a school counsellor or relevant professional may encourage them to openly discuss any issues and put them at ease.