Food - adult portions by the age of 12. No more kids meals in restaurants.
Clothes - adult clothes cost more but on the other hand they last a bit longer, most of DD's 2019 winter clothes still fit apart from trousers. Same with shoes, most last a lot longer than during younger years.
Secondary school uniform is eyewatering expensive in her school. Other school stuff like stationary, equipment, bags etc are more costly and need more replacement. Some books or workbooks need to be purchased.
Entertainment - she loves going to the cinema or coffee shops with friends. While she pays for some with her pocket money we subsidise.
Travel - no more kids fares or kids prices in hotels. She is too old to share a room and 2bedroom apartements cost a fortune. But too young for a room on her own.
School trips. They are less often but do cost more.
Certain hobbies - DD is a Scout, they go away on camps and activities. This is obviously voluntary but it is part of the whole idea and they are easy between £50-100 per weekend.
Other hobbies died down due to time restrictions so for us it is a bit of net gain = zero scenario.
In our area it is nearly impossible to get a job if you are under 16, most shops don't offer it due to red tape and what is available is often snatched up by students from the local college. Schools here also discourage them due to the sheer amount of school work they have to do. So not really any luck in earning their own money.