National Youth Violence Prevention Week in April will give Boston school children the chance to flex their creative muscles on a serious topic . A hip-hop video contest will be held for high school students, and the grand prize includes four Red Sox tickets, with the video spotlighted on a local radio station. A poster contest is planned for kindergartners through fifth-graders. Middle school students are encouraged to write poems reflecting an antiviolence message. The week runs April 7 through 11, with the winners announced on April 10. Deadline for entries is March 10. The events have been organized by Boston police, the Suffolk district attorney’s office, Boston Centers for Youth and Families, Suffolk County Sheriff’s Department, the US attorney’s office, and the Boston public schools.