How to write age when you are three and a half years old?

3-year-old and a half children 4 1 month. Because the baby is full-term after birth, the month age generally refers to the full moon, and the period from 0 to 30 days is 0 months old. Month age refers to the first month of the full moon, and every day after that is January or February, and so on.

One year 12 months x3 years =36 months; Half a year and six months, ***42 months, 30 days after deducting the age of 0 month, then the three-and-a-half-year-old baby is 4 1 month.