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.
Common characteristics include youthful appearance (youthful looks or childlike features) or emotional traits like innocence, naivety, or a childlike demeanor, often accompanied by a sympathetic flaw that the character strives to eliminate (clumsiness or a serious illness), although ultimately fails to achieve.