Final answer:
Children with Down syndrome have difficulty with in-hand manipulation skills mainly due to smaller hand size and absent palmar creases, as these physical traits affect the ability to move and control objects within one hand.
Step-by-step explanation:
Children who have Down syndrome may struggle with in-hand manipulation skills due to several factors associated with the disorder. The correct answer to the question is option 2: "Smaller hand size and absent palmar creases." Down syndrome is characterized by physical growth delays, distinctive facial appearance, and varying degrees of intellectual disability. This genetic condition is due to an extra chromosome 21 (trisomy 21). While almond-shaped eyes are a typical physical feature, they do not directly impact in-hand manipulation skills. Intellectual disability may contribute to various learning challenges but is not the main reason for difficulty with fine motor skills such as in-hand manipulation. Instead, smaller hand size and anomalies like the absence of palmar creases can significantly affect the ability to move and control objects within one hand, hindering the development of these fine motor skills. It is important to address these specific physical traits when considering therapies and interventions for improving manual dexterity in children with Down syndrome.