By PERRI KLASS, M.D. Published: September 12, 2011  What makes a child nap? Most parents cherish toddlers’ naps as moments of respite and recharging, for parent and child alike; we are all familiar with the increased crankiness that comes when a nap is unduly delayed or evaded. But napping behavior has been somewhat taken for granted, even by sleep scientists, and napping problems have often been treated by pediatricians as parents’ “limit-setting” problems. To read more of this article please click here to go to the NYTimes.