Aida Hernandez felt sick. The 2-year-old — who earlier had been nibbling on a cookie she found on the grass outside her home — could barely walk. So her parents took her to a hospital near their apartment in Longmont, Colo., where she spent the remainder of New Year’s Eve. Doctors conducted a toxicology screening, which showed Aida’s urine tested positive for tetrahydrocannabinol, the active ingredient in marijuana. Apparently, she had been chewing on a pot cookie