The raid - called "absurd" by one teacher - happened Friday night at One Tree Hill Kindergarten in Auckland, New Zealand's largest city.
As parents and the gaggle of children blasted the theme song to "Bob the Builder" and the "Chicken Dance," an irate neighbor spoiled the fun by calling noise control.
Teacher Jenny Skerritt said Tuesday that officers - who were "a little red faced" - suddenly appeared at the door with a noise abatement notice.
Skerritt said there was some noise, but not enough to disturb several babies, who snoozed through it all.
"I don't think it was that ragey, but it's all a matter of perspective I guess," she told National Radio.
They wound down the sound for the last half hour of the disco, which finished at 7 p.m.
The annual disco had never before attracted any other noise abatement complaints, said head teacher Lisa Gordon, adding "we're planning to frame the notice."