1. Height and weight development 1. What is the average height and weight of a three-month-old baby? 2. How fast does the height and weight of a three-month-old baby grow? 3. How to judge whether the height and weight of a three-month-old baby are normal? At three months of age, your baby\’s height and weight will increase significantly. According to statistics, the average height of a three-month-old baby boy is 61.5