Article 41 of the UNCRC says that the Convention doesn’t limit the rights children and young people have. Countries are free to give them more rights than the Convention lists; they just can’t take away the rights that are given by it.
It’s important to remember that the rights listed in the UNCRC are a foundation on which governments can build. They’re not intended to be goals to strive for or the most that children and young people can accept: rather, they’re the minimum that’s needed for them to live a safe and happy life.