For you - take lots of photos of them with you if you have space, maybe show them that you are packing them that way they know that you will be thinking about them too. What about getting them to choose something of theirs that you can take o/s with you (again space permitting) like a small stuffed toy that you can say goodnight to everynight (I know that probably sounds dumb) and then they can pick one that they can say goodnight to every night so it's like you're saying goodnight to each other...if that makes sense. same with the pre recorded messages, maybe you could do one that they can watch before they go to bed.

Love the map idea, could you do a basic itinerary with them and mark on the map where you will be on certain days so they can kind of travel with you. I think the calendar is great too, gives them a specific timeframe that they can see how long you will be away for, and also gives them things to look forward to before you get back.

Enjoy your trip, try not to miss them too much!