New Zealand's oldest mother, Lyn Mason, and her husband Ian tell Denise Irvine how they cope with their young family and other people's curiosity.It's a few days before Celine Mason's birthday, and when asked what she'd like as a present, she replies promptly, "a little pony".This is not of the four-legged, ride-on variety, but the brand of My Little Pony toys popular with girls, and Celine would like to add another one to her collection. She fishes in the toy cupboard and shows some of her favourites.Big brother Dean, 8, had his birthday in July, and he got a Star Wars Lego set that he's obviously...