I forget where it is said, but Cersei sees Bran and realizes that he does not remember anything.
Also, these theories:
- They thought he would die. Not a good theory since they already know he is alive.
- They thought no one would believe him since he was practically no one.
- They thought that it didn't matter since people already no about the rumor about Cersei and Jaime.
- They think that his memory is completely wiped.
They also have more important things to do. The rumor is already out so them trying to silence him would be illogical.
More to the point they have bigger fish to fry, an he doesn't intimidate them.
A qoute:
Jaime Lannister: I think we can outfox a ten year old.
Cersei Lannister: And my husband?
Jaime Lannister: I'll go to war with him
if I have to... they can write a ballad about us, "The War for
Cersei's Cunt!" [Cersei slaps Jaime. He chuckles, and she tries to
slap him again, but he grabs her arm and holds her from behind, firmly
Cersei Lannister: Let me go...
Jaime Lannister: Never.
Cersei Lannister: Let me go...
Jaime Lannister: [whispers
reassuringly in Cersei's ear] The boy won't talk. And if he does, I'll
kill him, Ned Stark, the king, the whole bloody lot of them until you
and I are the only people left in this world. [Cersei and Jaime
quietly sink into a loving embrace]
westeros.org:
The two are caught having sex by Bran Stark, and when Cersei insists
that they must do something to prevent the boy from telling anyone,
Jaime immediately pushes him off a tower.[8] She later berates Jaime
for his impulsiveness, arguing that attempting to kill the boy was
foolish when they could have simply intimidated him into silence.
Its futile killing him when everyone already knows what he will say. Plus, they might think he is scared. Most of his family is dead or missing.
SFF.SE Who knows the parentage of Cersei's children?
It wasn't a Lannister
? Isn't Joffrey 100% Lannister? – Shevliaskovic Aug 26 '14 at 6:24