My husband was also gone for seven months before he came home for R&R. Our daughter was only 18 months old when he left. We did several things that I think were a great help. First, she had her own picture of Daddy that she could have whenever she wanted and that she said goodnight to eveynight (she would even kiss it though I wouldn't push that unless your son wants to). I didn't know this at the time but you can also order something called a "Daddy Doll" which is a pillow whose cover is a full length image of Daddy. I have several friends who have done this and say it has been great. I believe the website is daddydolls.com.
My husband also made videos of himself reading some of her favorite books so she could have bedtime stories with Daddy. We made some before he left and he made some while he was gone. I don't know if they have that type of facility where your husband is but he could ask or maybe someone else there has a video camera they would be willing to share. Even just video where it is obvious he's talking to the children would be great.
I also tried to get her revved up about Daddy coming home. Whenever it would get close to time, we would sing and chant about "Daddy's coming home ! Hoorah!" No particular song or tune just anything to show I was excited so she could be excited. We also decorated the house and made signs and pictures.
I want to warn you to be prepared for some of the stresses. Zoe flipped whenever Mike left the house once he came home (even for good) especially if he had on his uniform. Your husband may need to plan some extra time before he goes out to reassure the kids that he is coming home later that day. She tested him a lot for a while after he got home. He had to be very patient.
I'm so glad this time is coming to a close for you. I remember how hard it is. I hope some of these ideas help. I would also urge you to use them with your daughter too. When I look at her bithday I see she is pretty little too. She remembers him but she may still feel a little shy for a while.
Good Luck!!!