"You must put on your heavy vests", the police in Gouda were told via the control room.
A witness had reported that a boy in a group in the Korte Akkeren district stood with a firearm in his hand and aimed it at passers-by.
Officers with service weapons drawn arrested three boys aged 14 and 15 near the Guldenburg.
On CCTV footage from the area, the police saw that it may have been a firearm.
There would also be fighting.
Several officers held the suspects at gunpoint.
The boys were arrested, searched and transferred to a detention center.
However, the 'firearms' that the boys were carrying turned out to be water pistols painted black.
"A stupid move that could have had major consequences," the police wrote on Facebook with a photo of the 'weapons'.
"Without black paint, they would have remained just water pistols. With the black paint, however, the story could have ended very differently."