Parents, schools and some doctors are voicing concern about children’s access to marijuana-laced snacks, which are becoming increasingly popular in states where recreational or medical marijuana is legal.

In Colorado, where recreational marijuana for adults ages 21 and older is now legal, marijuana-laced snacks are becoming a booming business, according to The New York Times. Products include chocolate-peppermint Mile High Bars and peanut butter candies infused with hash oil, the article notes.

Retailers say the products are popular with customers who want to experience the effects of marijuana without smoking and coughing. Critics say the snacks are ending up in the hands of teens who want to get high discreetly, or children who don’t know they contain marijuana. They note products can contain large concentrations of THC, the psychoactive ingredient in marijuana.

Colorado has ordered stores to sell marijuana-infused snacks with child-resistant packaging, and has banned labels designed to appeal to children.

In a study published in May 2013, researchers at Colorado Children’s Hospital reported they treated 14 children who ingested marijuana, half of whom ate marijuana-laced foods. Symptoms, most of which were mild, included unusual drowsiness and unsteady walking. One 5-year-old boy had trouble breathing. Eight children were hospitalized, and two were treated in the intensive care unit. All of the children recovered within a few days. The study was conducted after medical marijuana became legal in Colorado, but before the state legalized recreational marijuana.