But it is when he strides up to a home, dressed in shorts, sandals and a polo shirt, and knocks on the door that his detective work really begins. He tells the suspected violator that a neighbor has complained and he asks gentle questions to get to the bottom of things, all the while peering around for signs of youthful activity. His work is helped by a simple reality: children are hard to hide.

They leave tracks and make unique sounds. Newborns bellow, toddlers shriek and teenagers play music that is not typical around Sun City.

Mr. Szentmiklosi and his fellow child-hunters have their work cut out for them. The number of age violations in Sun City, a town of more than 40,000 residents outside Phoenix, has been rising markedly over the years, from 33 in 2007 to 121 in 2008 to 331 last year, a reflection of a trend at many of the hundreds of age-restricted communities nationwide.

This year’s figures are expected to be even higher, said Mr. Szentmiklosi, who knows that despite his patrols Sun City is probably harboring more children that have not yet been detected. The economic crisis is aggravating the problem, he said, forcing families to take desperate measures to cut costs, even if it means surreptitiously moving into Grandma and Grandpa’s retirement bungalow.

The vigorous search for violators of Sun City’s age rules is about more than keeping loud, boisterous, graffiti-scrawling rug rats from spoiling residents’ golden years, although that is part of it. If Sun City does not police its population, it could lose its special status and be forced to open the floodgates to those years away from their first gray hair.