"Oh Ella," Harry said. "It's not your fault your Mummy is sick. Some bad people made lots of people sick. Your Mummy unfortauntly was one of them. I was sick for a long time too and I got better." Of course he hadn't been as bad off as Millicent currently was.
"The sickness then made your Mummy lose the baby not you." He hugged her tighter. "There is no way little you caused your Mummy to lose the baby. I promise you." He told her as he kissed her hair.