The height of a child is measured from the top of the head to the bottom of the heels. The height of a child under 5 years old is measured when the child is lying down, so it is also called length. The average height of an 11-month-old boy is 74.5 cm while a girl of the same age is about 73 cm. Therefore, an 11-month-old baby of 70 cm is below the standard reference value.