St Barnabas Church in St Barnabas Street was damaged twice in two nights and has now cancelled their Little Frogs session on Thursday.
The most recent incident happened between 8pm on Monday, January 7, and 7am on Tuesday, January 8, when offenders smashed a window at the side of the church, possibly using a wooden bench from the nearby school.
The window was lead-framed and was made up of 18 smaller panes of glass, of which 12 were smashed and the frame damaged beyond repair.
No entry was made to the church.
A police spokesman said: “There was also an attempted break-in the previous night (Sunday 6/Monday 7) when offenders tried to break in through the door, causing damage.
“On this occasion, milk was taken from the doorstep.”
Witnesses to either incident, or anyone with information or who may have seen any suspicious activity in the area, is asked to call Northamptonshire Police on 101.
Alternatively, they can contact Crimestoppers anonymously on 0800 555111.