Anything that has to do with a person's growth and development is developmental. A baby's developmental needs include lots of interaction with parents and caregivers.
New parents are often conscious of developmental milestones, or stages, that a child achieves as she grows. By the time a baby is three months old, she's usually reached developmental goals like smiling, bringing her hands to her mouth, and tracking objects and people with her eyes. Each of these milestones shows how the baby is developing, or growing.