Ayda Field felt "powerless" when her son battled health problems.
The 'X Factor' judge - who has daughters Teddy, six, and Coco, two months, and son Charlie, four, with husband Robbie Williams - admitted "nothing else in the world" mattered when the youngster was ill with an unspecified condition.
Speaking at the Pride of Britain awards about Child of Courage winner Ella Chadwick - who was born with a rare kidney disease and has undergone two transplants - Ayda said: "My son's had health problems.
"Nothing as serious as Ella's, but when your child is ill you feel so vulnerable, so powerless.
"Nothing else in the world matters until they're well again.
"So I really felt all Ella's mum's worry and pain.To see Ella so strong, sweet, selfless and cheeky, is so uplifting."
Meanwhile, just weeks after welcoming Coco into the world via a surrogate, the 39-year-old actress recently admitted she'd already been talking to the 'Rock DJ' hitmaker about having another baby.
She recently said: "I wouldn't say no to four. I've been asking for another one already. You have to ask. After that the shop would be closed. We'd be in a people carrier and we'd be done. It's been a miraculous experience and I'm super-grateful and if I can convince him for four then drinks are on me."
However, the 44-year-old singer didn't seem as keen because he doesn't want to be an old parent.
He said: "Teddy's asking for another one. Ayda's doing subliminals, I just don't know, I'm going to give it a few months to see how I feel.
I know people are having kids a lot older in life but when Coco's 30, I'll be 70.
"I'm 44 and my mum's still here, she's in her late seventies and I know how quickly life goes, and I'd like to be around for my kids."