What is an appropriate milestone for a 6-month-old girl who is exclusively breastfeeding and gaining weight appropriately?

At six months of age, infants typically display a variety of social and emotional milestones, one of which includes responding to social interactions with smiles. Smiling when someone looks at or talks to them reflects the development of social engagement, indicating that the child is beginning to recognize and respond to familiar faces and voices. This social responsiveness is an essential aspect of emotional development and is a key milestone for babies around this age.

While the other options suggest important developmental skills, a six-month-old may not yet fully demonstrate those abilities. For instance, while lifting arms to be picked up can occur around this age, it may not be as consistently observed across all infants. Looking for their name is also a milestone that may be expected slightly later, and rolling over is a physical milestone that develops as infants acquire stronger muscle control. Thus, the ability to smile in response to interaction is the most appropriate milestone for a 6-month-old with the described developmental profile.