Because I have two children with additional needs.
Picture my family out for a walk. What do you see? A girl in a very large buggy, a tall pre-teen walking close by his Mum and telling her all about his latest video game, a lovely young woman, at a slight remove, headphones firmly clamped over her ears, and me, a middle aged Mum with a look of perpetual worry stamped on my face.
Perhaps you look a little more closely. You realise that the girl is actually a giggly teenager with a big bobbing head, tiny hands and feet, and the frill of a nappy peeking out over her leggings. Eeuugh, you think, she must be incontinent.