Hi Dana,
I don’t think you need “curriculum” at this age. I would concentrate on reading to your child, learning the letters and when he is ready the sounds that the letters make individually. You may use manipulatives and “ABC” type books for this or you can just use the story books that you read to him and point out the letters to him. You can also easily print some coloring pages for ABC’s for free online and make your own preschool type binder of these worksheets to take along with you wherever you go. I wouldn’t go the “official school books” route until he is older. When they are young, reading, talking, observing and creative play are much more useful, IMHO. You can simply use storybooks for your “phonics” during your overseas time. He won’t be behind or need to rush to catch up on anything if you do things simple. Both my school aged Dc did things mostly this way from 3-5 and this is the way I am doing things with my 4yo dd currently. You won’t know at what age and in which way your child will be ready for learning these types of things. Start small, easy and simple, in the most natural way you can think of and go from there. Since you will be with you ds, you will know when he is ready to start learning letter sounds, tracing letters on a page, etc. He may not be ready for more complicated phonics such as consonant blends and silent letters and such until he is older. 6 or so. If you are going to be coming back before he turns six then you should be able to have a better idea of where he should start and what type of methods he would respond to best.
This went longer than intended! I hope it made some sense, though. Blessings
P.S. Don’t sweat it during these early years. Focus on habits first, then read to him a lot, encourage him to think, talk and discuss things with him and observe him so that you know what he is ready for and when.
-Miranda