There are three reasons why you and your peers may have different amounts in your child trust funds when you reach 18.
You may have started with a different amount. The scheme changed over time so those born later generally were given less. How much money your family had also affected how much the government gave you.
Friends or family members may have added additional money.
There are many different types of child trust funds. Your parents will have chosen a fund or this may have been allocated on your behalf. Different funds performed differently, meaning some went up in value more than others.