If the rash is occurring on cheek in 3-4 months old child is most probably due to atopic dermatitis which is dry irritated skin condition resulting in itching and oozy skin. This might also effect other body parts like face, neck, front of elbows, back of knees and child might become irritated. It has to be managed with syndate bars or soaps, proper moisturizers, avoiding the irritants and oral or topical steroids. Proper consultation with dermatologist is advisable.