What is a common developmental milestone for infants?

Responding to their name around six to nine months is considered a common developmental milestone for infants because it signifies their growing awareness of social interactions and their environment. At this stage, infants begin to understand that they are separate beings from their caregivers, which is crucial for their social and emotional development. This response to their name often indicates that infants are becoming more attuned to the language and sounds used by those around them, setting the foundation for further communication skills.

Other options present developmental stages that either do not typically occur within the specified timeframe or are not recognized milestones. For instance, walking independently by three months is beyond typical motor skill development for infants, as most begin walking closer to twelve months. Speaking full sentences by twelve months is also unrealistic; at that age, children usually start to say single words or basic sounds rather than complete sentences. Recognizing strangers at three months may happen but is not a reliably observed milestone, as stranger anxiety typically develops closer to six months or later. Thus, the correct answer reflects a realistic and widely acknowledged milestone in infant development.