The Strongest Junior High School Student

Zhang Xiaohua, a child who just graduated from junior high school. (Graduating in 2021) Just when he was about to play games happily, his mother suddenly came into his room, confiscated his mobile phone, and said she would return it to him when he started high school. The child then died suddenly and painfully. Then he was reborn. Mainly, why was he reborn as a kindergarten graduate? After traveling through time, he also acquired a useless system. We are junior high school students and we want to be the strongest elementary school students!