The most common features include youthfulness as a physical trait (younger age or pigtails) or as an emotional trait such as a naive or innocent outlook, a childlike personality, or some obvious sympathetic weakness the character works hard to correct (extreme clumsiness or a life-threatening disease) but never really succeeds to get rid of.
Typical attributes include youthful appearance (youthful looks or childlike features) or emotional characteristics such as innocence, naivety, or a juvenile personality, often accompanied by a sympathetic weakness that the character attempts to overcome but never succeeds in eradicating.