Are you looking for speech to text capability or can he type?
We did a big trip a few months ago. Since we took the kids (then 8 & 6) out of school for a month we made them actually write in an old school paper journal but DH and I also did a blog that they contributed to as well. There was spell checking built in and we put a few pictures each day. Not sure if that would work or if you want something more kid friendly.
DS's android tablet has decent speech to text which he uses quite a bit. We didn't try this but I'm guessing we could cut and paste that into a blog (or whatever else).
