My child is constantly touching his genitals...
Children become aware of their genital organs towards the end of the first year. Touching their genitalia is a normal extension of the way they explore the rest of their bodies. Over time, children realize that handling their genitals is pleasurable.
Is my child masturbating?
No, not in the sense that we (adults) understand the word. In some children, handling may become more like fondling that takes on the overtones of real masturbation. There are many misconceptions about masturbation. Masturbation is not something to be embarrassed about, either in children or among adults. It is neither abnormal nor unusual. It does not lead to homosexuality, "nervous weakness" or physical debility.
Should I be concerned?
There is no need for concern. Your child is not a pervert. Masturbation in young children is rarely done with any purpose or for any length of time. The pleasure the child derives is almost incidental, rather than sexual. Do not reprimand your child for this normal behavior. You will make him feel ashamed and it will probably result in his continuing to masturbate furtively. He will probably never discuss his genitals or sexuality with you in the future. The best way to deal with this is to ignore it. If it happens in public, distract your child, but under no circumstances, take him to task.