One of the biggest problems I have with WLS for children is that they cannot give informed consent. Not only can a minor not give consent, legally (their parents have to do it for them), but I don't believe that young people have the life experience and knowledge base to make that kind of decision.
There are a number of things that minors are not permitted to do, even with a parent's permission. They cannot get tattoos, drink alcohol, see certain movies, and, in some cases, have sex (especially with a partner who is not a minor). There are very good reasons for age limits on these things. In the case of tattoos, and some kinds of piercings, it is a way to protect that young person from doing something to their bodies that cannot be undone, and which may have negative consequences in the future.
Does that sound familiar? Now, to be fair, a tattoo is hardly comparable to WLS. After all, a tattoo is highly unlikely to leave you with diseases associated with malnutrition or kill you. Tattoos can be removed, albeit expensively, even years later. And, a tattoo does not require you to adhere to a strict daily dietary regimen that may be difficult for a young person to stick to. So, even if your mom gives you permission to have Tweety Bird tattooed on your ankle, it's only logical that you should not be legally permitted to do so until you are an adult, while she can happily sign off on getting your stomach amputated. Right?
Other types of legal restrictions exist to protect children from themselves, or from negatively impacting others around them. Young people need time to develop their bodies and minds. A 13-year-old who gets pregnant is more at risk than an 18-year-old, whose body is more prepared for pregnancy and childbirth. Young people need their decisions tempered with guidance, with veto power by a mature person, so that they are not punished for life by consequences of immature decisions (such as the aforementioned barely-teen mother). The same 13-year-old is also more at risk for getting an STD from a sexual partner, because she is not yet experienced or educated enough to take precautions. Why is it that these types of things are widely recognized as not age-appropriate for young people, but it's regarded as a-ok to have children undergo high-risk surgery to "solve" a problem that is not an emergency? If your daughter came home and said, "All the other girls are getting pregnant, and I want a baby of my own," you would do everything to dissuade her, and tell her that bowing to peer pressure to do dangerous things is a bad thing in the long term. Actually, you'd say, "If they were all jumping off a bridge, would you do it too?"
"Informed" is a key word in informed consent, as well. Not even adult patients get a proper education about the risks. WLS proponents are so gung ho to make a buck that they don't want to scare off their gravy train by telling them how it is. And while they can explain it to the parents, it isn't fair to foist the procedure on people who are too young to have the education and experience to put the information into context and understand the ramifications of WLS. A young person who is dealing with the social stresses of being fat will also be very eager to do anything to change that situation--even claiming that they are ready to make the rather intense lifestyle changes necessary to survive, but these same kids told mom and dad that they really truly would feed the hamster/dog/parakeet and clean its cage--and we all know how that turns out.
Simply put, it is not right or fair to have children undergo WLS when they are not even able to properly consent to having a tattoo because it is assumed that they might regret it later. I guarantee that if the tattoo and piercing industries started lobbying to eliminate age requirements, people would be in an uproar. WLS can have much scarier consequences, and the industry behind it is pushing hard and fast to get their hands on kids' bodies. If you are a parent, you SHOULD be in an uproar over that.