Oh, but to answer the question that the SAB poses regarding the number of "sons" God has, you have to look at the subtleties of the language and the theology. Note that the verses calling Jesus God's only son actually say "only begotten son," and that word is important. Every other being called the "son" of God was either created by God ex nihilo, or was "adopted" into His family. In a sense, all human beings are God's children, but this terminology is talking about a special relationship, as is the relationship we find a few chapters from here between Abraham and Isaac, where I'll probably talk a little bit more about this.
Back to God's actual words in that sandwiched verse, He says of mankind that "yet his days shall be an hundred and twenty years." The SAB points this out as a possible contradiction to a verse in the Psalms claiming that men live to be only seventy. There's a lot that can be said about this. One thing is that of course either number being thought of as an estimate of how long a person might live is clearly an average. Not every man is going to live to be exactly 70, many will die young, some will live to be well over a hundred, so any specific counterexamples to this number are hardly breaking the general rule. It may very well be that the life expectancy at the time around the flood was quite different. Before the flood, we see the average life span of those people whose ages are given is right around 900 years old, while after the flood, the life span seems to quickly drop to about half of that, and continues dropping, tending towards the lower 100s (although admittedly never quite getting there). But lifespans aside, there is another possible meaning to this verse, and I think it's a likely one. When God says "yet his days shall be an hundred and twenty years," what He may in fact mean is that the flood is going to come 120 years after the events being talked about here. Note that in the end of chapter 5, Noah is 500 years old, and the flood comes when he's 600, so it may be that the story is saying, "Around the same time that Noah was raising Shem, Ham, and Japheth, there was some stuff going on in the world that was making God very unhappy."
So what was making God so unhappy? I'll engage in some slightly wild speculation aided by verse 4. We've got giants, we've got "sons of God", and we've got some notable sexual unions happening. What is this all about? Believe it or not, it's a fairly commonly accepted concept that what's happening is procreation between human females and fallen angels. There is a theological doctrine that says that before the world was created, some of the angels in Heaven decided to rebel against God, and God kicked them out. (As some have pointed out to me, a lot of this we owe to Milton's "Paradise Lost" more than the Bible, but there is some Biblical basis for it.) After the fall, these creatures managed to gain free access to earth. The whole idea related to this short passage is that some of them figured out how to have sex with humans, and eventually, they somehow had children that, for whatever reason, were giants. (In the Hebrew, the word nephilim, translated "giants" actually comes from a root word meaning "fallen" or "cast down". It's also used in Numbers 13:33, where it's much more clearly referring to giants.) This was apparently an important part of the whole problem of the earth that led to God causing the flood.
Let me finish today's post with a look at verse 5, and what the SAB says concerning it. I think it's odd that in comparing this verse to 8:21, it's cited as an absurdity rather than a contradiction, but I guess sometimes it's a personal judgment call. Here, God says He's going to destroy every living thing because of the evil of men's imaginations, in the later verse, God says He's going to be nicer because of the same thing. I think you have to look at 8:21 more carefully.
And the LORD smelled a sweet savour; and the LORD said in his heart, I will not again curse the ground any more for man's sake; for the imagination of man's heart is evil from his youth; neither will I again smite any more every thing living, as I have done.Note that God doesn't say that He won't destroy the world because of this evil in men's hearts initially; He first says He won't "curse the ground". I think this primarily hearkens back to the curse from chapter 3, which given this verse, may in fact show to be more of a punitive thing than I had said in my commentary there, but it's hard to say. In any case, I think the point that God may be making here is that the world keeps growing steadily more and more evil, and in the end, evil is largely its own punishment. Why does God need to add any more of a burden on to the life of man to remind him of the fallen state of the world, when mankind has to live with itself day after day? Not that things will be rosy and cheery and all good, but that things are just going to be largely left to their natural processes. Furthermore, in the case of the flood, which is tacked on as an ending clause to this verse, I think God is saying that once is enough.