Police said more charges were expected "pending the outcome of further inquiries".
A court hearing might be held later today at Hutt Hospital where the woman was recovering from injuries sustained during her arrest.
A nine-year-old boy hurt during the incident was recovering in Wellington Hospital and was in a stable condition, police said.
Three other victims have been discharged.
"While the laying of charges is an important step in the inquiry, there is still a lot of work to be done regarding the ongoing investigation," Detective Senior Sergeant John van den Heuvel said.
"In the meantime, we have a large team working on the inquiry and are strongly focussed on finding out what has happened," he added.
"We again reassure the community that we are not seeking anyone else in relation to this tragic event, which is an isolated incident, with no ongoing risk to the community."