In the last paragraph of Andrew's Brain by E. L. Doctorow:
MT’s invented silliness at his children’s bedtime. How he is their protector, and the world’s a safe snug place at their bedtime. How when they are grown they will remember this tale and laugh with love for their father. How this is his redemption.
What is meant by "MT’s invented silliness at his children’s bedtime"?
Does it mean that he invented some silly, happy, childish stories and told them to his children?
The Chicago Tribune explains:
Andrew is a fan of Mark Twain and mentions that he reads Twain's stories out loud and views his work as "company." Doctorow concludes his book with Andrew thinking about his daughters, and how Twain "invented silliness at his children's bedtime." When his daughters grow up, he thinks, "they will remember this tale and laugh with love for their father. How this is his redemption."
So, yes, you're right, and 'MT's' (Mark Twain's) 'invented silliness' refers to the silly stories he must have conjured to tell his kids at night.
(There are a number of articles online that talk about Mark Twain having invented stories for his children to be told at bedtime; in fact, a book was later published.)
