This week, I will take the police to court for kettling me and my friends. On 24 November 2010, we joined thousands of other schoolchildren, walking out of our classrooms and going to central London to demonstrate against education cuts. We protested peacefully but we were imprisoned in Whitehall by the police for up to 10 hours, on one of the coldest days of the year, with no food and very little water. Because I was afraid of being kettled again, I didn't go to the next two demos and many children, including my fellow claimant Sam Eaton, have not gone on another protest since.

I found it inspiring to see so many young people attending the demonstration, prepared to stand up for what they believe in. But it saddens me that the police can crush this young movement's motivation and scare children off attending future demonstrations.

As under 18-year-olds, we are unable to vote. One of the few opportunities we have to make our views heard on decisions that directly affect our lives is through protest. Some people say that children should not go on protests, but that is ridiculous. We should not be denied the right to march and let our opinions be known. We are not politically apathetic; we fully understood the government's proposals of nearly trebling university tuition fees and abolishing Education Maintenance Allowance (EMA). Nobody voted for these changes, and now they are being challenged as illegal in the high court by two sixth-form students.

I am part of a young generation fully engaged in those issues – we care about our future. We all want to live in a society where everyone's views and concerns are taken into account. It is a success for democracy when children are involving themselves in politics. We cannot let the police quell children's right to freedom of expression.

What's more, the law is on our side. The United Nations convention on the rights of a child recognises the importance of children being heard. That convention, with the European convention on human rights and the Children Act 2004, place obligations on the police to facilitate children's right to protest and to promote and safeguard their welfare. Today, in the high court at a judicial review, I, with Sam Eaton and my younger sister Rosie Castle, will argue that the police failed to meet these obligations when they decided to imprison shivering schoolchildren.

The recent declaration that the G20 kettling was illegal showed that kettling must only happen in truly extreme and exceptional circumstances, there must be good reason to believe that there will be a breach of the peace and the kettling must be proportionate to this breach of the peace. A few windows being broken, after the kettle had been put in place, does not justify locking anyone up, especially children.

This has to be seen as part of a wider picture, which includes the mass arrest of peaceful UK Uncut protesters in Fortnum & Mason and the arrests on the day of the royal wedding. This is the criminalisation of dissent, and in a healthy democracy it cannot be allowed to go unchecked. Everyone has a right to freedom of expression and the right to protest. For children, this is especially important. We cannot sit back and let the police ignore these rights.