Events to which students invite grandparents or special friends are very popular and produce good attendance.

You can allow every student to bring a guest to lunch throughout the week and have students puts on a nutritional lunch program.

Incorporate presentations by students about what they are studying. Invite guests to read to kids or be read to by kids. Host an "Invention Convention," and let students explain what their inventions can do, why they built it and how. Provide a music performance. 

There are many options, but remember that personal invitation by individual students guarantees attendance. Connecting childless community members with elementary and high school students is a positive move; remember that it will require some lead time.