WAUKESHA, Wis. (AP) — Four staff members at a Waukesha child care center were taken into custody while investigators looked into allegations of physical abuse.

According to Waukesha police, three staff members at The Lawrence School were booked and released Wednesday on potential charges of failure to protect and the fourth person was arrested and taken to the Waukesha County Jail on possible child abuse charges.

The center closed early Wednesday and police worked most of the day to reunite children with their parents.

“The investigative team developed a plan to substantiate and moreover have access to key personnel and pieces of evidence,” Waukesha Police Capt. Dan Baumann said in a statement late Wednesday. Baumann said the school was also found to be operating at over 150% of its state-regulated capacity.

“Investigators were able to have access to family members as well as the children to seek out other potential victims in this case. With this being an open and active investigation, we will refer further questions to the criminal complaint which will be forthcoming.”

The Lawrence School serves children ages 6 weeks to 12 years old. It also provides before and after school care for the Waukesha school district.

Police are working with the Wisconsin Department of Child and Families, the state Division of Criminal Investigation, the Waukesha County Sheriff’s Office and the district attorney’s office.