Our family has gone through two Naval deployments so far. Our children are still young, (3 and under), so I knew when my husband left that it would be nearly impossible to reason with them, or explain his long absence in a way they could understand. Instead, I decided to focus on making Daddy a constant presence in their lives through photos, video, and audio.
We used three tools with our kids: a Daddy video, a Daddy audio tape, and a Daddy book. Every morning while the kids ate their breakfast, they would watch their Daddy video on my computer, which was simply a video I had put together in iMovie using a bunch of my husband's photographs. After a few weeks of this, our sons actually began asking to watch the Daddy video as soon as they woke up in the morning! At lunchtime, I had them listen to an audio tape my husband had recorded before he left, on which he read five of their favorite books. And several times throughout each day I would read to them their Daddy book, which was a book I made using construction paper, and photos of my husband - pictures of his face, as well as pictures of him with our sons. It was a very simple book, with phrases like, "My daddy is brave", and "Daddy loves me!", etc.
Every day I told them that Daddy was at work on a ship, and that he would be home soon. When he finally did return home, our children recognized him, without a doubt. Even though they may not have been able to understand his absence, Daddy was a daily presence in their lives, and they did not forget about him.