Here are two interviews, where George tells what he thinks about what Jaime did to Bran.
https://www.huffingtonpost.co.uk/entry/game-of-thrones-season-3-characters_n_1854918?guccounter=1 :
"Obviously a lot of people, when Jaime throws Bran out the window, and we like Bran, we've seen his good points, tend to think that makes Jaime a bad guy. But then you understand, if you understand the situation, if Bran goes back and tells what the saw, and is believed, Jaime will be put to death, his sister will be put to death, and there's an excellent chance that his own children will be put to death.
So I said to my friend, what would you do if some other eight year old kid was in a position to say something and you knew that would mean the death of your own young daughter. And he said, that eight year old kid is dead! And this is what we would consider a moral man.
So how do you make that choice? The abstract of the morality vs. the lives of your own children. I mean, I don't know that I'm a prostelitizer who says this is the answer to that, but I have to question the painful, difficult question, the difficulty of the choice, that's what I think makes powerful fiction."
https://www.rollingstone.com/cultur...-r-martin-the-rolling-stone-interview-242487/ :
"At the same time, what Jaime did is interesting. I don’t have any kids myself, but I’ve talked with other people who have. Remember, Jaime isn’t just trying to kill Bran because he’s an annoying little kid. Bran has seen something that is basically a death sentence for Jaime, for Cersei, and their children – their three actual children. So I’ve asked people who do have children, “Well, what would you do in Jaime’s situation?” They say, “Well, I’m not a bad guy – I wouldn’t kill.” Are you sure? Never? If Bran tells King Robert he’s going to kill you and your sister-lover, and your three children. . . .
Then many of them hesitate. Probably more people than not would say, “Yeah, I would kill someone else’s child to save my own child, even if that other child was innocent.” These are the difficult decisions people make, and they’re worth examining."