CHICAGO (AP) — With virtually no hard proof that medical marijuana benefits sick children, and evidence that it may harm developing brains, the drug should only be used for severely ill kids who have no other treatment option, the nation's most influential pediatricians group says in a new policy. Some parents insist that medical marijuana has cured their kids' troublesome seizures or led to other improvements, but the American Academy of Pediatrics' new policy says rigorous research is needed to verify those claims. To make it easier to study and develop marijuana-based treatments, the group recommends removing marijuana from the government's most restrictive drug category, which includes heroin, LSD and other narcotics with no accepted medical use, and switching it to the category which includes methadone and oxycodone. Studies have linked recreational marijuana use in kids with ill effects on health and brain development, including problems with memory, concentration, attention, judgment and reaction time, the group's policy emphasizes. [...] the marijuana movement has grown substantially.