Final answer:
Infants develop the ability to hold their head upright and steady, roll from side to back, sit up with support, and hold their head steady by the end of the fourth month. By age three, children have developed gross motor skills for climbing and climbing stairs, as well as fine motor skills for handling objects and doing puzzles.
Step-by-step explanation:
During the first two months after birth, an infant normally develops the ability to hold their head erect and steady when they are held in an upright position. They will also develop the ability to roll from their side to their back. By the end of the fourth month, the infant can roll from front to side, lift their head 90 degrees while lying prone, sit up with support, and hold their head steady for brief periods (Figure 23.5.9).
By the age of three years, children have reached the end of the toddler stage. They have the gross motor skills needed to climb and climb stairs one foot per step. They also have the fine motor skills needed to handle small objects and to do simple puzzles.