Ferrets are increasingly popular as pets, but the weasel-like animals can be dangerous to young children, two doctors say. In three unprovoked attacks, two babies had their ears bitten off by ferrets and required constructive surgery and a third infant suffered scratches and bites requiring 39 stitches, John W. Paisley and Brian A. Lauer write in today's Journal of the American Medical Association. ``Two of the children were asleep in their cribs when they were bitten,'' the two University of Colorado School of Medicine doctors said. ``Although ferrets are increasingly popular pets, we believe that they are not suitable pets for families with small children,'' said the doctors, who claim Americans own more than a million ferrets and are buying them at the rate of 50,000 a year. All the babies recovered, the doctors said, adding that reports of severe injuries caused by ferrets are few. But ``a ferret may bite so tenaciously that it has to be pried off or killed to loosen its hold,'' the doctors said. One of the animals in the attacks described had to be killed before it would release the child, they said. The incidence of ferret bites is unknown because most states do not require bites to be reported to health officials, the doctors said. During an 11-month period in Arizona, the ratio of reported bites to the estimated pet population was 0.3 percent for ferrets, compared with 0.4 percent for cats and 2.2 percent for dogs, they said. Sale or ownership of pet ferrets is prohibited in California, Georgia, New Hampshire, New York City and Washington, D.C., the doctors said. A ban also has been proposed in North Carolina.