Officials at the St Anna Church in Ascheberg, south of Münster, were horrified to discover the destructive rampage, which saw statues and other religious artefacts damaged.
“This was serious vandalism,” said parish secretary Marlies Stratmann.
The vandals struck between 3:30pm and 5:40 pm on Tuesday. As well as urinating in the holy water, they also broke four statues of apostles in the knave of the church, as well as damaging a bishop's staff, two swords, an incense burner and the church's newly renovated pipe organ.
Several wreaths were stolen, one of which was found in a nearby school playground. Children returned it to the church, Stratmann said.
The cost of the damage totalled several thousand euros, church officials estimated.
A spokesman for the nearby Coesfeld police said that “children or youths” were viewed as likely suspects.