Will Smith often struggles with parenting his three children because they stopped listening to him ''a long time ago''.

Will Smith's children no longer listen to him. The 47-year-old actor is father to sons Trey and Jaden and daughter Willow, but says his brood have stopped taking advice from their parents now they are grown up.

He said: ''You know, listen, I have a 23-year-old, a 17-year-old, and a 15-year-old, so they were done listening to me a long time ago.''

Will's latest film 'The Concussion' sees him star as Dr. Bennet Omalu, a pathologist who makes history when he uncovers the link between permanent brain damage and the frequent head injuries professional footballers suffers from.

Shooting the film, which is based on a true story, made Will even more aware of the dangers of the sport, and he admits watching the finished movie as a parent was a harrowing experience.

He told Us Weekly magazine: ''It was a little scary because my son played football for four years, and I wasn't -- it [brain injuries] never even was a subject. It never came up. We were concerned about him breaking his leg, or spinal injury was the big thing that all of the parents were concerned about. So it was scary to me -- it was almost as if it was hidden in plain sight. And as I started to understand the science, I knew that it was something that I wanted to deliver to the world.''

But when it comes to forbidding his children from playing the game, Will knows it's easier said than done.

Asked if he would still let his kids play football, Will answered: ''I'm glad that that's a hypothetical question. Anybody that has kids, you know how hard it is to tell your kids, 'No.' So if he wanted to play, I would want him to be thoroughly informed, and as a family we would have to make an informed decision.''