The height, fatness and thinness of the baby as it grows is a concern for the mother. At a certain age of months, the baby’s weight and height will change. So, what are the indicators of baby development in three and a half months? 1, weight: the average weight of male babies is about 6.4 kg, the normal range of 5.0 to 8.0. female babies weigh about 5.8 kg, the normal range of 5.0 to 6.5. 2, length: the average height of male babies is about 61.4 cm, the normal range of 57.3 to 65.5. female babies are about 59.8 cm, the normal range of 58.2 to 62.0 About. 3, head circumference: the average head circumference of male babies is about 40.8 cm, the average head circumference of female babies is about 39.8 cm. Ability indicators: 4, body movement and control: when lying prone, the baby can use forearms and elbows to support, head and shoulders raised, chest can leave the bed. 5.Abilities that should be mastered (most babies can do it): able to recognize your face and smell; can hold his head up steadily; eyes can follow moving objects. 6.Developing ability (half of the babies can do it): can scream, make “giggle”, “coo” sound; can spit bubbles; recognize your voice; can do small push-ups. 7.Advanced ability (only a few babies can do it): can roll over from prone to supine; can turn their heads to look when they hear loud noises; can put their hands together and slap toys with their hands.