Yuch. I'm sorry! As a military wife/mom of 3 kids (ages 15, 11, 1) and one on the way in June:
Things I've found that help with kids is:
1. (I know Target, I'm sure other) Stores have a little water-proof photo album - the one at Target says "Who loves Baby" - that you can fill with pictures of Daddy so your son can carry that everywhere with him. If Dad sends new pics, you can switch them out. It's great for conversation, too.
2. A video of Daddy reading a favorite book or telling him how much he misses him, etc.
3. A calendar (maybe big, hand-drawn or computer printed or project-sized from Office Depot) that stickers can be placed on each day to visualize the passing of time.
4. Conversations with Daddy - webcam, letters, phone
5. You talking to him. Don't be afraid to cry in front of him (not ALL the time, of course - but if it happens a few times, don't feel bad) or talking "I really miss daddy, too. I miss when he _______ or _____ and _____" "I wish daddy were here. He'd really like what we're doing right now." "Daddy will love that picture."
6. Let your son send mail to daddy. Encourage your husband to talk about the mail via webcam, even (it feels interactive and relevant). for example: "I LOVE this picture you drew and sent me!" as he holds the picture up and looks at it. Let your husband give ideas via webam for activities for you and your son go do afterward: "Maybe you and mom should go to the library today. Then you can tell me all about it." It gives a feeling that dad is still a very active participant in your lives.
FYI- There is a support, too. If you live close to Aberdeen Proving Grounds or Fort Meade (many other bases also have) a branch of PWOC - Protestant Women of the Chapel. At Fort Meade we meet weekly on Wednesdays from 9am to noon. You can be involved in friendships, good food, and Bible Study. You can find contact info on Myspace: PWOC.
I hope this helps.