The onset of puberty begins. The sex hormones become active, manifested in behaviour and physical development, but also in perception and emotional mood swings. Girls usually reach puberty two years earlier than boys. Obvious physical changes include the growth of breasts and an increase in height.
From about the age of 10, children become more interested in adult sexuality. They fantasise more about sexuality and hear and see all sorts of things in books, on TV and on the internet, which arouses their curiosity. Nevertheless, their response may be prudish or offhand if you try to talk to them about sexuality.
The first steps towards love may be taken during this phase: young people start going out with one another and make cautious advances towards one another (holding hands, kiss on the cheek, etc.)