The crackdown on retailers that sell liquid nicotine used in e-cigarettes escalated Tuesday as the New York attorney general reached a settlement with four businesses that failed to secure the potentially toxic substance in child-resistant packaging.

The move by Attorney General Eric T. Schneiderman came a year after the state passed a law requiring retailers of liquid nicotine to better secure the substance, which was blamed in the death of an 18-month-old boy in New York last year. Poison control centers across the country have received hundreds of calls after children have come in contact with the liquid, which can lead to serious illness or death if swallowed or absorbed through the skin, health officials said.

Liquid nicotine, a key ingredient in e-cigarettes, is taken from tobacco and infused with flavors, colors and chemicals. Health officials worry that the resulting products, sometimes packaged like candy, can appeal to children.

Many state legislatures have acted or are considering action to rein in the sale and marketing of e-cigarettes, a growing business that has been largely unregulated despite the serious health concerns associated with it. Last year, after the Food and Drug Administration proposed regulations for e-cigarettes, Mr. Schneiderman and 29 other attorneys general called on the agency to restrict companies from marketing and selling e-cigarettes to minors and to ban flavored e-cigarettes.