Here’s what Professor Hallux has to say:
WOW – that’s a big question today! Despite what you may think, the difference boys and girls isn’t whether you like football or fairies – and I happen to like both! It’s buried deep in every cell of your body – inside the chromosomes!
Chromosomes are packages of DNA and they’re the instruction books for your cells. The instructions that make you either a girl or a boy are written in these packages. Around the ages of 8 to 13 a part of your brain called the pituitary gland releases chemicals called hormones, and these start to change your body to become an adult man or woman – depending on which set of instructions are in your chromosomes.
These changes are called puberty. And as well as your body changing to look more grown-up, there will be changes inside which in time will mean you can have babies of your own. If this sounds weird, just remember every single man and woman on earth was a boy or a girl once – just ask your Mum and Dad!