Jada Pinkett Smith thought she'd be dead by the age of 21.

The Madagascar 3 star - who raises Trey, 19, Jaden, 14, and 11-year-old Willow with husband Will Smith - admits turning 40 in September 2011 was "surreal" because she grew up in such a tough neighbourhood, she never expected to live so long.

"I grew up in a drug-infested neighborhood where you walk out each day and you just hope that you make it. I came from a war zone. There was a possibility that I wouldn't make it past 21 - that was the reality. When I turned 40 it was a surreal moment because I had never imagined reaching 40. I looked at my husband and said, 'Oh my God, I'm 40! What am I going to do now?' So yes, it does put things in perspective."

Jada - who was raised by her drug-addicted mother Adrienne and grandmother Marion - is thankful her own children don't have the upbringing she had and she has no idea how she would cope if she were in her mother's situation:

"I'd be terrified if I had to raise my kids in the environment I grew up in. When I look at them, I see them flourishing at such young ages and I wish to God I could have had the luxury to sit back and think, 'Mum, I want to go out and get my vocal lessons today because I have this new song that I want to write.' What I had to think about was, 'Oh man, I wonder what I'm going to eat tonight because there's no food here. How am I going to get to school? And is my mum going to be OK today? Will this be one more day she survives her addiction?' That's the kind of stuff I had to think about at 11."