Birthdays

Jack just had his birthday. He's a big kid now. The conversation the whole day was about his party, and the other kids' plans for theirs.

It started out ok.
Jack: It's my birthday!
Me: Really? Wow etc
Nicholas: I'm going to your party hey Jack?
Jack: Yep.
[Followed by all the other kids checking to see if they were coming. Jack going around the table saying everyone's names and that they could come.]
Me: Can I come?
Jack and Nicholas exchange glances: No. [Cheeky grins.]
Me: [Very disappointed.] Why not?
Jack: [Searching for a reason.] Cos no girls!
Me: What about T?
Jack: No, she's a girl.
Me: What about A?
Jack: No, she's a girl.
I refrained from telling him I was having a girl's only party and he couldn't come, so there.

Clearly I missed a bit, because when I came back from my break, they were all at late afternoon snack, and Jack and Nicholas were telling everyone they saw that:
"Sexy boys and sexy girls are coming to my party."

I really should have asked for a definition.