It is not too harmful. It has proved benefits. Children and adults have the choice. It is not affecting anyone else but their family. Why do people believe they have the right to say what people can do in terms of medicine. What is bad is people believe that ivory etc have medical benefits, some how that's legal, to kill animals for that reason but god forbid using medical cannabis.
If children develop a terminal illness such as cancer, and begin to experience incurable pain, parents should act to help alleviate their children's pain if possible. If medical marijuana is an option that relieves pain sufficiently for life to be bearable, the parents should have the right to choose that option for their child. Medical marijuana also comes in pill form, so this doesn't necessarily mean helping a child smoke.
No, parents should not use medical marijuana for their children's illnesses, because marijuana is dangerous. Children who use marijuana very young will likely become addicted. Most parents are not doctors and do not appreciate the harm that they are putting their children in by exposing them to this drug at a young age.