Melabie, I just saw a special on tv talking about this subject last night. Sesame Street is doing a series about this subject. Unfortunately I only could watch it for a couple of minutes (in between getting twin 21 month old ready for bed) but they suggested doing a couple of things that I will list:
(1) placing alot of pictures of him around the house to remind them what their dad looks like.
(2) doing a daddy and me board, which is a poster board full of pictures of things that they did together. You can either send it with their father,keep it at home or both. It is something they can talk to you about when they miss their dad.
(3) trace their hands amd make a hand slash or necklace for him to take with him so when he gets home-sick he can wear it. Also you can make a picture frame using their hand traces as well, and put a picture of all three of them and send it to him when they get miss daddy (this is my idea).
I hope these ideas will help you and if I can help you in anyway (or anyone else) please do not hestitate to write me.
God Bless you and your family and I will be praying for his safe return.