A priest raped a seven-year-old girl while visiting her in hospital after she had her tonsils removed.
Another priest forced a nine-year-old boy into having oral sex, then rinsed out the youngster's mouth with holy water.
One boy was forced to say confession to the priest who sexually abused him.
An estimated 300 Roman Catholic priests in Pennsylvania molested more than 1000 children - and possibly many more - since the 1940s, according to a scathing Pennsylvania grand jury report released on Tuesday.
The report accused senior church officials, including the man who is now archbishop of Washington, D.C., of systematically covering up complaints.
The "real number" of victimised children and abusive priests might be higher since some secret church records were lost and some victims never came forward, the grand jury said.
US bishops adopted widespread reforms in 2002 when clergy abuse became a national crisis for the church, including stricter requirements for reporting accusations to law enforcement and a streamlined process for removing clerics. But the grand jury said more changes are needed.
"Priests were raping little boys and girls, and the men of God who were responsible for them not only did nothing; they hid it all," the grand jury wrote in the roughly 900-page report.
Cardinal Donald Wuerl, leader of the Washington Archdiocese, was accused in the report of helping to protect abusive priests when he was Pittsburgh's bishop from 1988 to 2006.
Wuerl has disputed the allegations.
At a Mass held Thursday in Washington on the feast of the Assumption of Mary, Wuerl did not address the accusations against himself but urged parishioners not to lose confidence in the church over the "terrible plague" of abuse.
Australian Associated Press