Two nuns who worked for decades at a Catholic school in California embezzled a “substantial” amount of money from tuition and other funds and used it to pay for gambling trips to Las Vegas, church officials have said.

Sisters Mary Margaret Kreuper and Lana Chang are believed to have siphoned off cash from tuition fees and donations at St James school in Torrance, near Los Angeles, for at least a decade. Neither has been charged with a crime.

Kreuper was the school’s principal and Chang taught eighth-grade students before the pair both retired this year.

A spokesman for the archdiocese of Los Angeles, Adrian Alarcon, said the alleged theft was discovered during an audit, routinely held after a principal leaves office.

The total taken from the school was still being calculated, Alarcon said, adding he could not confirm reports that it was up to $500,000 (£400,000).

In a letter to parents, Monsignor Michael Meyers described the sum as substantial. “This matter came to our attention during financial reviews in connection with the change in leadership at our school,” he said, adding that no one else was implicated.

At a meeting he is reported to have told parents that around the same time as the audit, a family requested a copy of a cheque made out to the school and staff noticed it had been deposited in a bank account that was not the school’s.

Meyers said both nuns acknowledged the theft when confronted, apologised and were cooperating with an investigation. He said they and their order, the Sisters of St Joseph of Carondelet, had promised to pay back the money.

“Sister Mary Margaret and Sister Lana have expressed to me, and asked that I convey to you, the deep remorse they each feel for their actions and ask for your forgiveness and prayers,” Meyers said in his letter. “They and their order pray that you have not lost trust or faith in the educators and administrators of the school.”

The archdiocese has notified the police but Meyers said church officials did not plan to press charges and instead wanted to resolve the situation internally with the money repaid and the nuns disciplined by their order.

However, some parents are reportedly angry at the route being taken and are trying to band together to push for criminal charges. “We were an ATM, and people know it and they won’t ask for justice,” Jack Alexander, a parent with a child at St James, told the Southern California News Group.

He said parents knew the nuns went on gambling trips but the sisters claimed a wealthy uncle funded them. “These nuns took a vow of poverty and said, ‘Oh, no, we’ve got a rich uncle,’ ” said Alexander. “The rich uncle was the parents of the St James students.”

Another parent, who did not wish to be named, told Fox 6: “I will honestly say that it’s not shocking to me. There have been a couple of projects that we have been trying to get funded for many years that we have unfortunately been unable to move forward with because of the lack of funding.”

But for others, the idea of a nun stealing money was difficult to believe. Samantha Pierce, whose son also graduated from the school, told the Press-Telegram: “They [the church leadership] convicted the sisters before they actually have the facts on hand, that is the thing that disturbed me the most.”

The school was struck by tragedy in 2014 when a driver killed four people, including a six-year-old boy, who were leaving a Christmas concert at the school. She later admitted vehicular manslaughter with gross negligence.

Kreuper and Chang worked at the school for 29 years and 20 years respectively.

Neither nun could be immediately reached for comment.