The singer attended a festive event at Great Ormond Street Hospital to meet young patients as they received gifts from Santa Claus.
Bunton hugged the children and posed for photos, and admitted the day was especially upsetting as she is a mother of two young sons.
She tells Britain's Daily Star newspaper, "Great Ormond Street Hospital has a huge place in my heart and it's lovely to be here to meet so many parents and patients.
"For a couple of hours they get to forget their illnesses, have fun with their siblings and act like normal kids should do at this time of year.
"As a parent your heart just goes out to them and the bravery they show. It is so wonderful to see all of the children and an absolute honour for me to attend."