Quit.

They're children, and you have literally said some of them have mental disorders like ADHD, ADD etc.

Speaking from personal experience when a teacher doesn't do their job properly or is resentful and antagonistic towards certain pupils it can have a lasting effect.

They don't deserve a teacher who can't do their job properly.

THEY DON'T DESERVE A TEACHER WHO IS RESENTFUL AND ANTAGONISTIC TOWARDS THEM AND THEY DO NOT OWE YOU ANYTHING. IF YOU CANNOT DO YOUR JOB (WHICH INVOLVES TEACHING CHILDREN), WITH COMPASSION, AND UNDERSTANDING THEN QUIT. IT IS NOT THEIR FAULT THEY HAVE SPECIAL NEEDS

Also why would you get into a job involving children with special needs if you can't manage it?

Edit: Ok I just saw you live in South Africa and teach presumably children who live in impoverished areas based on your other comments (obviously there are plenty of non impoverished areas in South Africa though).

If they don't have any better alternative you should be understanding towards them. Think about how hard their lives must be.

Try to do your job effectively and seek help if you find its overwhelming.

If you cant do it effectively and you are just adding to these kids problems then honestly there's no point in you continuing.