Identify other local schools and after-school programs by asking friends and coworkers. Once you choose a school or program, call to set up the visit. At a school, try to speak with the science teacher or science department chair. It is more direct than asking for the principal or guidance counselor. At an after-school program, ask for the youth programs director or group leader.
Teachers are hard to reach during the day.
If you leave a message, make sure to include your home phone and appropriate calling hours. If it is convenient for you, ask whether e-mail is a better way to communicate. Explain that you are interested in visiting the class or program and leading hands-on activities related to engineering. Whether there is an engineering topic the teacher would like you to cover or introduce. How old the children are and how many are in the group.