She said she “found the wealth gap and the race gap” in the US “really difficult”.
In an interview with ES Magazine, she said: “I didn’t want to bring my son up there. There were things I couldn’t grasp, for example once I had a call from my son’s nursery letting me know the sniper drill went well. They do that regularly, wheeling them out in their cots.
“Over here in the UK, I understand the problems. There are lots of calls you might get from a nursery in London but that ain’t going to be one of them.”
Jumbo, 36, said she was hugely influenced in the way she was bringing up her son by her own father, who stayed at home to look after the children while her mother worked.
The actress, whose son Max is three, said of her father: “He did traditionally female roles. He isn’t afraid to cry but he is also incredibly disciplined.
“That spectrum of a man is something you want your son to have, especially now. Being disconnected from your emotions and not being able to express them is not going to serve you well.
“ I hope my son doesn’t get to five or six and not think he can be silly anymore or fall over and cry.”
Jumbo’s career was transformed when actress Christine Baranski saw her one-woman New York show about dancer and civil rights activist Josephine Baker. Baranski offered her a role on The Good Wife, which carried on into the spin-off series The Good Fight.
The actress also credits Baranski with the best advice she ever received on motherhood. She said: “She told me that everything costs something and once you make peace with that it stops being a game of guilt with yourself.
“When you leave the house to do a job you have to commit 110 per cent and forget you are a mum. My phone is on airplane mode at work unless it’s an emergency contact.
“Then when I get in the door I am 100 per cent there for Max. I try not to beat myself up about it but of course you f***ing do.
“I missed his first steps, his first words, never took him to his first day of anything. But I want him to understand that your parent is a whole person and the more he sees me fulfilled the more he will love me as a mum.”
The star, who is preparing to play Hamlet at the Young Vic, added: “Anyone who says they can juggle work and parenthood is a liar.”