A new swine flu strain recently sickened two pre-school children in Pennsylvania and Indiana, but they cautioned that the cases appeared to be isolated, Federal and state health officials have said. Both the children recovered, however, and there is no evidence that the virus is spreading easily among people, meaning that it does not appear to pose a threat of becoming a significant public health concern, officials said. \"We want people to be aware of these things, and we want physicians to be aware,\" according to him. Both children are 2 years old. In one case, a boy in Indiana was apparently infected by a caretaker who had been showing pigs at a county fair a few days before the boy became ill. In the other, a girl in Pennsylvania appears to have been infected when she went to a county fair and petting zoo