Is tickling babies' tummies good or bad?

I don't think there's any effects on tummy tickling and I strongly agree with Hui Qun. Some babies squeal in glee and giggle if you tickle their tummies but I've seen some who cried so hard when tickled. Play by the ear, if the baby is giggly and happy okay fine but if the baby's just stoning at you and his mouth is upturning, please stop unless you will be the one to calm the baby down and not his mother.