Why can’t Stella play?

M: Hi, you’re new here, aren’t you? What’s your name?
W: Stella.
M: Want to come and play?
W: I’d like to. but I can’t. My Mum says I’ve got to stay and help her. It’s my brother’s birthday and we’re having a party, too.
M: Oh, you’ve got a brother, haven’t you?
W: I’ve got two brothers. Kit, the one with the birthday, he’s only four. I’ve got a big brother who’s married, his name’s Don.
M: Does your brother Don live near here?
W: Yes, not very far away. Cathy, my sister-in-law, works in the sweetshop over there. They’ve got a new baby called Liz. I mean Elizabeth really, but we call her Liz.
M: Is that your Mum over there calling you?
W: No, that’s my Aunt May, my Mum’s twin sister. I’d better go. Bye.
M: Bye.