Hi B.! I can understand what you're going through - my family was a Navy family, and my father was gone typically 3-9 months a year most of my life.
A few things that could be helpful would to have lots of pictures of your husband around, and if you can, one small one per child for them to hold onto. That way, they get to see Daddy everyday. Depending on the kind of online access you have with him, you may think about joining a service like Skype, which would allow you to do free calls over the computer and if you each have a webcam, see each other.
The kids could make pictures for daddy, and he could write them letters about what is going on with his life while he's gone. I still have about a dozen letters my dad wrote me over the years that I treasure about his trips to Spain, Italy and the Middle East. We would also dedicate a few crafts to dad - when he came home, we would decorate him with macaroni necklaces, paper ties, and the like.
Good luck!