In Colorado, the combination of decriminalizing medical marijuana and declining federal prosecution was associated with a significant increase in the exposure of young children to marijuana. Physicians, especially in states that have decriminalized medical marijuana, need to be cognizant of the potential for marijuana exposures and be familiar with the symptoms of marijuana ingestion. This unintended outcome may suggest a role for public health interventions in this emerging industry, such as child-resistant containers and warning labels for medical marijuana. The consequences of marijuana exposure in children should be part of the ongoing debate on legalizing marijuana.