What is the most likely diagnosis for a child with symptoms consistent with seborrheic dermatitis?

Seborrheic dermatitis is characterized by red, greasy patches of skin covered with yellowish scales, often seen in infants as cradle cap or in areas with high sebaceous gland activity. The condition commonly presents in areas such as the scalp, face, and behind the ears. Its symptoms align closely with those described, making it the most likely diagnosis.

The other conditions listed have distinct features that set them apart. Contact dermatitis typically exhibits an acute inflammation due to an allergen or irritant, resulting in red, itchy rashes that may be localized to areas of contact. Psoriasis presents with thick, silvery scales and usually occurs on extensor surfaces and the scalp, often accompanied by systemic symptoms and nail involvement. Eczematous dermatitis is characterized by dry, itchy, and inflamed skin that can appear anywhere on the body and usually has a more chronic course. The specific signs and locations of lesions described in this question clearly align with seborrheic dermatitis, solidifying it as the correct diagnosis.