It's a difficult question. Not only sex reassignment operations, but also hormones which are also prescribed as part of the process or changing gender can have a permanent effect on a person's body, in adults as well as children but especially somebody who is growing as it may restrict the development of secondary sexual characteristics. Which is exactly what a transgender person would hope for. Seeing themselves develop into "the wrong gender" as they hit puberty can be very frustrating and alarming for them. After all, what girl wants to start getting broad shoulders and a hairy chest? And what boy would like to start growing breasts? Hormones, either oestrogen or testosterone, can prevent that from happening. The problem is that some people, having taken hormones for a while, change their minds and decide not to follow the path they have embarked upon. A child or adolescent may find that the changes that have occurred are irreversible. At the moment in the UK there is a very long waiting list of several years to be seen at a gender clinic. These clinics provide both counselling and practical assistance. Children should be referred to these clinics for advice, but not necessarily medicine or surgery.