Good looking sons you have there. Just as RBnSC says take lots of pics, tell them you love them. If Mrs. has time have her put together some scrap books so you have stories to share vs. a box of photos with faded memories.
Time flys and before you know it they will be doing their own thing. Mine 2 are off serving in the military now USN and USMC yet they both made it home for Christmas. Good to have them back even if a short time.