(Reuters) – A group of Flint, Michigan, parents and their children filed a class action on Monday alleging that gross negligence by Michigan Governor Rick Snyder and others caused the city’s drinking water to become contaminated with lead.

The lawsuit was filed in Detroit federal court and seeks damages for a proposed class of “tens of thousands” of Flint residents and property owners who have suffered physical or economic injuries. The named plaintiffs are seven residents and their 17 children who lawyers say have heightened lead levels.

The state’s slow response to the water crisis drew sharp rebukes from Democratic presidential candidates Bernie Sanders and Hillary Clinton on Sunday. Both called for Snyder’s resignation. A spokesman has said the Republican governor has no intention of stepping down.

Flint, a predominantly black city of 100,000, was under the control of a state-appointed emergency manager when it switched its water source in April 2014 to the Flint River from Lake Huron. The more corrosive river water caused lead to leach from city pipes and into the drinking water.

The city switched back last October after tests found high levels of lead in blood samples taken from children, but the drinking water has not returned fully to normal. Flint began replacing lead pipes running to homes on Friday.

Attorneys Hunter Shkolnik and Adam Slater allege in Monday’s lawsuit the governmental defendants failed to take measures required by federal law to eliminate the dangers and downplayed the severity of the contamination to residents.

Children are especially vulnerable to lead exposure, as even small amounts can stunt development, leading to lifelong academic and behavioral problems.

Current and former officials and workers in Michigan and Flint are named as defendants, along with engineering firm Lockwood, Andrews & Newnam, which was hired to assess the feasibility of using Flint River water.

A firm representative said the lawsuit mischaracterized its role and it would vigorously defend its position in court.

The lawsuit accuses the governmental defendants of gross negligence, which is an exception to the immunity that shields federal and state governments and employees from lawsuits over their official duties. The strength of the immunity defense has kept many leading plaintiffs’ lawyers away from filing lawsuits over the Flint crisis.

The families seek payment for past and future health costs and monitoring as well as compensation for lost property value, replacement of pipes and reclamation of contaminated property.

(Reporting by David Bailey in Minneapolis; Editing by Anthony Lin and Matthew Lewis)