The Government has a responsibility to act in the best interest of each child and not discriminate based on their parents (and that includes rich parents, it is there in black and white).
Do you mean Article 2, which is the only one referencing discrimination?
1. States Parties shall respect and ensure the rights set forth in the present Convention to each child within their jurisdiction without discrimination of any kind, irrespective of the child's or his or her parent's or legal guardian's race, colour, sex, language, religion, political or other opinion, national, ethnic or social origin, property, disability, birth or other status.
2. States Parties shall take all appropriate measures to ensure that the child is protected against all forms of discrimination or punishment on the basis of the status, activities, expressed opinions, or beliefs of the child's parents, legal guardians, or family members.
I really don't see how VAT on a paid service aimed at children is discrimination. NB I searched for 'tax' in the charter and couldn't find a reference.
The (UK) State arranges for provision of an education to all children living in the country, regardless of social origin, status etc of the child or their parents. That would seem to cover the obligations in Article 2.