They were joined by fellow pop stars Rochelle and Marvin Humes to spread some festive cheer at the Great Ormond Street Hospital bash.
Former Spice Girls star Bunton was seen cuddling up to a young girl in a wheelchair as they posed for pictures, and she later wrote on Twitter.com, "Always amazing to see everyone @GreatOrmondSt Christmas party! you all, you're all so strong and brave."
Girls Aloud singer Roberts sat down and helped the children decorate some cakes while posing for photographs with the patients, and The Saturdays singer Rochelle Humes later tweeted, "Lovely afternoon at the @GreatOrmondSt Christmas party. Thanks so much for having us! So lovely to see you all x"