Trying to get a young child to understand why their daddy isn't at home is a tough job; one that I never wish on anyone. When my husband was gone last year (for 9 months), it was a daily battle to help our two year old son understand that Daddy was just doing his job and would be back with us soon. Naturally, some days were better than others.
For the most part, I think that being able to Video Chat and Skype with his daddy helped our son out the most. While it wasn't always convenient, it was a huge asset to be able to let them interact on the computer. Our son is big into Hot Wheels Cars and Toy Soldiers, so I always put a few little toys in the husband's care packages that we sent so that they could "play" on the computer when they got a chance. We also had a countdown jar filed with Hershey Kisses. Each day, right before bedtime, our son was allowed to have one more Hershey Kiss and we talked about daddy coming home.
The most important thing, as someone mentioned already, is to keep busy. Occupy yourself and your child with hobbies and trips to the park. If you are okay, your child(ren) will be okay.