This reminded me actually that my DD and her baby cousin share a birthday too. It was DDs birthday a few weeks back and we got a message at lunchtime saying that they'd have to miss the party because baby had arrived that morning.
It was lovely news and we all went, awwww they share their birthday!
Saying that, DD had originally stolen the birthday thunder anyway because she was born on the new baby's Dads birthday too! So we have my DD, baby's Dad and baby all with the same birthday in our family.
Babies. Total bloody limelight stealers, the lot of them!