It’s a victory for Nanny Bloomberg.

After plumping up for decades, schoolkids here took the prize for the biggest decline in childhood-obesity rates of any large city in the nation, city officials boasted yesterday.

“It comes at a time when obesity rates for the nation’s children as a whole are stable or continuing to increase,” Mayor Bloomberg noted during a visit to PS/IS 218 in The Bronx.

A study by the federal Centers for Disease Control and Prevention found that the obesity rate among kindergartners through eighth-graders here fell from 21.9 percent in 2006-07 to 20.7 percent in 2010-11.