Stage of children by age neonatal period after birth 4wk perinatal period 28wk of gestation 1wk after birth infancy 4wk lyr Toddlerhood 2nd yr 3rd yr 儿学R的neonatal period after birth～ 4wk perinatal period 28wk of gestation ～1wk after birth infancy 4wk～ 1yr Todlerhood 2nd yr ～ 3rd yr Stage of children by age