More children are being sent into foster care as a result of the abuse of heroin and opioid painkillers, The Wall Street Journal reports. Officials say opioid abuse is straining child welfare agencies.

The number of children in foster care in the United States rose 3.5 percent from 2013 to 2014, reaching 415,129 in September 2014. While national data do not measure how many children arrive in foster care because of their parents’ drug use, some state and local officials say opioid addiction is a likely factor in the increase.

Experts tell the newspaper the overprescribing of opioid painkillers, along with a cheap and plentiful supply of heroin, has contributed to the crisis.

A Vermont state survey found opioid use was a factor in 80 percent of cases in which a child under age 3 was taken into custody. Governor Peter Shumlin said the number of children under the custody of the Department for Children and Families grew 40 percent over two years. The increase was driven largely by parents’ opioid addiction, he said.

The state tries to find an appropriate relative to care for children taken away from parents who abuse opioids. If they cannot find one, the state places the children with foster families, the article notes.

In Indiana, an estimated 2,600 children were removed from homes due to parents’ drug abuse in a six-month period that ended last March—a 71 percent increase from two years earlier. The state’s Department of Child Services has added 459 case managers in the past two years to deal with the increase. “I don’t think anybody expected the explosion of heroin,” Mary Beth Bonaventura, the agency’s director, told the newspaper.