My kids get £1 a week for every year of their life. So 4 years old gets £4 and 10 would get £10.
No, they don't have to earn it. They are expected to help out around the house and do little chores as and when because that is part of being a family and living together, not because they are incentivised financially.
Their pocket money goes onto their GoHenry cards and they all have the app and can see what money they have. One of my children saves up and rarely spends, they have a couple hundred on their card, they get a thrill out of seeing the saving grow. The other two the money comes in and is pretty much spent that day. I don't buy anything extra for them, if they want a comic, Smiggle, toys, Robux it comes off their card.