No the big bump is a vaulted head. That is actually a trait I am working for. I have noticed that even hatching babies from all vaulted parents, the percentage is about 30% vault to 70% regular poof!
Some of my first babies hatched were from all vaulted stock. A 33% ratio all the way. 4 had high vaults (the bump) 4 had small bumps and the other 4 had no bump at all. Now that their a bit older (5 months) all have nice puffy heads, and the vaulted in particular have a high rise hairdo. Ill try to get some pictures of my older kids and I will post them later.
I am fairly certain that both males and females though can have the vault, so you can't sex them that way.
Can you get pictures of your babies on here? I would love to see them.