Nearly two-thirds of all sexual assaults perpetrated by a female reported to ChildLine, a children’s helpline based in Swansea, South Wales, were by mothers, according to new figures by the National Society for the Prevention of Cruelty to Children (NSPCC).

Of the 2,142 young people sexually abused by women that the charity counseled last year, 1,311 admitted “they had been abused by their mother.”

The report found that during the past five years, there has been a 132 percent rise in reported sexual abuse by females. In contrast, sexual abuse by males during the same period rose only 27 percent.

ChildLine President Esther Rantzen said that this statistic is partly attributed to more boys calling the helpline than in years past—not necessarily more females abusing males.

Ms. Rantzen also said that “by listening to the direct and authentic voices of abused children,” her organization has broken the myth that sexual abuse not only happens to girls, but boys too.

“Mothers can sometimes sexually abuse their sons,” she said. “And the report found that when girls are sexually abused, by far the most common perpetrator is not a stepfather, as many believe, but the biological father.”

“Many would find it shocking that any woman—let alone a mother—can sexually assault a child,” head of ChildLine Sue Minto said. “But they do.”