As some of you may know,I am not a fan of the OT.
I have had some discussion about the OT with a few Jewish friends of mine, one of them is a reasearcher at the Center for Jewish research here in Toronto.
I asked about the issues with the plagues and while they were not THESE issues ( they were in regards to God hardening the heart of the Pharoah and why the death of the innocent children), thier response MAY be used to "explain" these issues too, but I think Leo made a good case alread:
They said, basically, that the writer(s) of Exodus out into words what they observed, what they saw first hand and such.
They knew that God had sent Moses and Moses has the power of God behind him so, anythign that happened MUST have been God's will to happen that way ( free will didn't really count for much in the OT it seems, with their view that God manipulated Pharaoh), in regards to the death of the 1st born of Egypt, what MAy have happened was that a virus killed many of the children of Egypt ( the hebrews being secluded weren't ALL effected but some probably were) and of course,under the circumstances, God must have sent it.