Online posts unfortunately do not disappear. So an 18 year old has to answer for his dumb 16 year old self. This is awful and makes me sad.
A wise primary school teacher told me that over his decades of experience he learned that many kids experiment with things that make them feel strong and powerful. He observed that they often had little to no understanding of what they were doing until they were guided. So a child using racist language may not be a racist, as much as he is trying on the power of a racist. It is the power that thrills him.
These are children. They can learn. The "racist" ones are exactly the ones that we should reach and teach.
The question really is what is redeemable vs what is not? You can decide for yourself. What instantly disqualifies a child vs what does not?
IMHO, educational institutions at all levels should be more generous and more forgiving because they are in the business of producing educated healthy adults.
If anything, we should focus more resources towards kids that are saying racist things. They are still kids. We can show them a better way.
Forgiveness is divine.
It is the responsibility of parents, teachers, adults and mentors to guide children away from mistakes towards the ability to make healthier choices.
Children also learn from their environment. Many of my college friends had never had anything spicy beyond a hint of black pepper due to their upbringing. Some thought spicy food was foul, unpleasant and foreign. It took them a few times visiting Indian, Caribbean, Thai, and Korean places to get hooked and completely change their world view.
We shouldn't mark kids as racist. Everyone has the capacity to grow and learn. Children especially so.