infantile flaccidity of muscle

例句：

1. 1. The infantile behavior of the child is quite unusual.
   这个孩子的行为很幼稚。
2. 2. Pediatricians are specialistsin treating children's diseases.
   儿科医生是治疗儿童疾病的专家。
3. 3.Juvenile delinquency isa serious social problem.
   少年犯罪是一个严重的社会问题。