There are other ways that this boy can receive the benefits of marinol without having to use cannabis. Cannabis is available in a regulated way from a pharmacy. People just want to smoke and use other products because it's more fun. It's safer, however, to have children go the regulated route and use a pharmacy.
No, we should not take effective medical treatments away from children. If a treatment is useful for a child, it should not matter whether or not the substance was arbitrarily deemed to be illegal. The only way the treatment should be assessed is whether or not it treats the child effectively.
Kids, like all humans, are entitled to medical treatment. There is no good benefit from removing medical care from children. If the question is whether children should be treated with cannabis oil, then the answer remains the same. The question of what treatment is appropriate for a particular child is best left to the parents and the child's primary care provider.
Medical treatments are important in the development of a child. When a child becomes ill has to be taken to the specialist to be evaluated and probably prescribed with a treatment to follow in order to overcome his/her sickness. There are also vaccines/shots that have to be provided on a regular basis to prevent the child form becoming sick. If other types of medicines or natural products are beneficial in the treatment or healing of a sickness, they can be used as complement to the medical treatment prescribed by a doctor.