Final answer:
Infants reach several developmental milestones throughout their first year, starting with smiling at 2 months, babbling and sitting at 6 months, and by 12 months, they may start to walk, understand simple commands, and say a few words.
Step-by-step explanation:
Infant Developmental Milestones
The developmental milestones an infant typically reaches at each age are significant markers of their growth and development. At birth, infants display basic reflexes and have the ability to respond to environmental stimuli. By 2 months old, a baby usually starts smiling and making vocal sounds. At 4 months, the infant continues to express delight and is keen on grabbing toys. When a baby reaches 6 months, they have usually begun babbling, sitting without support, and may exhibit stranger anxiety. At this age, their vision has improved considerably, and they might start making sounds like "mama" and "dada".
By the time an infant is 12 months old, they have reached several important milestones including the ability to stand with assistance and possibly take their first steps. They may wave goodbye, cooperate with dressing, and babble a few words repetitively. During this time, infants also begin to understand simple commands and enjoy playing games like drop and watch.
Throughout the first year, infants experience significant growth in both physical size and sensory abilities. They also start to cut their deciduous teeth, typically around six months. The timing of these developmental milestones can vary among infants, but they provide a general guideline for expected progress during the first year of life.