Which developmental sign would warrant further evaluation at 18 months?

At 18 months, a child's social and emotional development is a critical aspect to observe. The lack of attachment to caregivers is a significant developmental sign that warrants further evaluation. Attachment is essential for healthy emotional and social development in children, and difficulties in this area can be indicative of underlying issues.

Children typically exhibit attachment behaviors by seeking comfort, showing distress when separated from caregivers, and demonstrating joy upon reunion. If a child does not establish a secure attachment, it could lead to challenges in forming relationships later in life and may suggest deeper psychological or developmental concerns that need attention.

The other options listed—walking independently, climbing stairs, and speaking two-word phrases—are generally considered normal developmental milestones for an 18-month-old child. Walking independently usually occurs around 12 to 15 months, climbing stairs can be observed around the same period, and beginning to speak two-word phrases often develops between 18 and 24 months. Therefore, while these milestones indicate progression in physical and linguistic abilities, they do not signify the need for immediate further evaluation as deviations in attachment behaviors would.