I think my ds (14m) has an umbilical hernia. His tummy button used to be a perfect little bowl (even when he was the fattest lardy lump of a baby you ever did see) but just recently it looks like a bowl with a large scoop of ice-cream in it. the lump is soft and sometimes goes back in, depending how he's sitting, but if he's standing up it pokes out.
does that sound like a hernia to you?
what's the story with them? does he need a doc?