The double Oscar-winner is up for another Academy Award this year for his portrayal of US president Abraham Lincoln in the acclaimed biopic Lincoln - but says sons Ronan, 14, and Cashel, 10, barely bat an eyelid.
"They didn't even know what I was doing until a couple of years ago," he told The Daily Mirror.
"In fact, my 14-year-old boy was asked what I did and he said, 'I think he's in construction'. That's how much they know!"
Talking about his latest film, Daniel, 55, said he felt a connection with President Lincoln as he delved deeper into the role.
"There wasn't a day when I didn't feel grateful to be exploring his life," he said.
"I grew to love him in a way I didn't realise you could love a person you've never met."