Developmental milestones are physical or behavioral signs of progress in infants and children. Unlike growth, these are functional skills or age-specific tasks children can do at a certain age range.

By the time they reach 18 ... month-old is the ability to mirror the actions and sounds of others. Early attempts at a younger age likely include facial expressions during interactions or clapping ...

Children reach developmental milestones ... A baby is anticipated to begin walking at some point between the age of seven months and 17 months. If the child gets to be 18 months old, and is ...