Yes they can. You will need to re-enroll when you return. Here's the form to fill out for a long term absence.
https://www.fcps.edu/sites/default/files/media/forms/se291.pdf You will not be provided with any work for your kids to complete. Make sure you are having them do work so they will not be overwhelmed when they return to school in the fall. You can always follow information from the FCPS curriculum and find free/inexpensive things from the internet for them to do.