Hi A.,
I second the photo book idea. My dh is deployed this year so I made him a photo book at http://www.clarkcolor.com. I included poems, quotes, and a compilation of pictures of the kids from birth to now to include him with the kids, family trips and random photos I've taken since he's been gone that he hasn't seen. Most of the photos were black & white but I included some color ones as well. You can edit and change photo color with the photo book program. It was simple but time consuming mainly because I was deciding what photos to include.
In the past, I've also used 12x12 picture frame, a 12x12 scrapbooking acid free paper and given the kids my acid free pens to let them create. It didn't matter that he was little, that was the beauty of it. I used paint to make a hand print on the page and then I would add photos of their dad and them together. He's loved this and hangs it in his office.
One of my favorite gifts we made him is along the same lines as the photo frame. I used an 8 1/2 x 11 frame & scrapbooking paper. I selected one picture of ds with dad, used paint to make his handprint and then typed an "I Love You because..." list. I included things like ...you read me stories, ...you wrestle with me, ...you give me hugs and kisses, ...you tuck me in at night, ...you teach me things. I listed things that were unique to their relationship. This is by far his most favorite gift.
Good luck,
J.