During my husband's first deployment, my son was just a newborn. His only care was eating, sleeping, and crying for hours on end. The fact that his father was thousands of miles away probably didn't have much of a major affect on him at that time. When my husband redeployed, it really began to hit him just how much of our son's life he had missed. He left home with a pregnant wife and returned to a walking toddler. Over the next year, my husband did his best to make up for lost time with our son. The day he deployed again, our son was nearly 3. We had prepared our son for several months beforehand for what was to come, knowing he was too young to fully grasp the situation. We talked to him about it almost every night after prayers, explaining that daddy would be gone for a long time, but that he didn't want to leave us and that he would be home as soon as he could. A week before the deployment, we took our son out for a special day, just for him. Before the day was over, we visited Build-A-Bear, where my husband dressed the bear up in camos and recorded the bedtime prayer in his voice. We asked our son what he wanted to name the bear and he said, "Daddy Bear". We teared up right there in the mall :) Now every night before bed, my son makes sure he presses Daddy bear's hand and says his prayers with daddy and then gives it a kiss goodnight, just like he always did with daddy before. It is the one thing that really keeps daddy close to him when he's so far away.
If your child doesn't have their own "daddy bear", have no fear! There are plenty of alternatives out there for keeping daddy (Or mommy) close during deployments. Here's just a few I've found:
http://flatdaddies.com/ (If you cannot afford one, you can also apply to have one donated to you).
http://cool.canvasondemand.com/category/operation-hi-mom-honey/operation-hi-honey/ (Again, you can apply for a free one.)
Here's a photo of my son and husband building "Daddy Bear"