Final answer:
An 18-month-old child needing assistance to climb stairs upright while being able to crawl up stairs is consistent with expected behavior for that age. It is normal for toddlers to hold onto something for support when navigating stairs until about the age of three when further coordination and motor skills develop.
Step-by-step explanation:
While assessing an 18-month-old child, a nurse observes that the toddler can crawl up stairs but needs assistance when climbing the stairs upright. This behavior is indicative of expected behavior in a toddler of this age. By the age of two years, it is normal for toddlers to navigate stairs one step at a time while holding on to something, such as a rail or an adult's hand. Therefore, the developmental milestones of the child in question align with typical physical development benchmarks.
An 18-month-old child mastering the ability to crawl up the stairs shows progress in gross motor skills. It is not until around the age of three that children can climb stairs with alternating feet without support, which demonstrates further improvement in both gross and fine motor skills. The ability to navigate stairs without any assistance is part of a continuum of developing mobility and coordination. While talipes equinovarus (clubfoot), neurologic damage, or developmental dysplasia of the hip could cause persistent difficulty with stair navigation at older ages, none of these conditions is suggested based solely on the behavior described for an 18-month-old.