The singer-turned-actress said that motherhood opened her eyes to the problems that children from less financially stable backgrounds face.
She told InStyle, 'After I became a mum, I felt passionate about the fact that no child should go hungry. Food is not a luxury.'
The 30-year-old has since joined forces with international peace-seeking organisation the United Nations, and is an ambassador for its World Food Programme (WFP).
'Through my involvement, I've helped the WFP raise $12m (£7.7m) - that's a staggering 43.5 million meals,' she said.
'I've seen swollen bellies and hair that's turned white from lack of nutrition, and yet some of the people I've met have such optimism it's incredible. One kid in Haiti was telling me how he adores school. He never misses a day, he dreams of becoming a doctor.
'That sort of thing makes you want to work that much harder for those kids who truly want to succeed and rise above whatever they're going through.'