Playing against humans is definitely a thousand times more enjoyable, and also better to improve at go, than playing against a computer.
Many decades ago, I was 11 year old too. My parents let me play on KGS. I played a lot. They did not monitor me (or more likely they did, but I never noticed).
I did encounter disgruntled and rude players. When that happened, I talked about it with my parents, and also with my go teacher. They helped me understand what happened, why it happened, what I could have done to deescalate the situation, and most importantly, taught me to be less affected by it when it wasn’t my fault.
The world is full of sore losers, bad winners, and people whose actions or words are coated in bad faith. Better to meet a disgruntled and rude go player across a virtual go board, than a disgruntled opponent in a physical sports match; or, much later, a disgruntled and careless driver on the road.
I’ve also encountered disgruntled go players during real-life go tournaments. These people left a much stronger impression on me than the online players, especially when they were adults and I was in my early teens.
I don’t play video games, but from my friends who do, I understand that online video game communities can be pretty toxic, and much more harmful than a few impolite go players. I think that meeting the online go community is a good way to see how things can be when people are not toxic, and to avoid becoming rude oneself. If there is a chance that your kid is going to play online video games in a few years from now, then I don’t think you should shield them completely from the OGS community.
The world if also full of great people, bearers of kindness, altruism and wisdom. And hopefully your child will meet those people too.
You can enable Zen mode by default where there is no chat, but you then have to trust him that he does not disable it. Also there is the profanity filter, but that does not stop people from being rude.
With the profanity filter on, children think it’s fun to type bad words and see them get censored. Soon their chats are full of them, and they don’t know that other people can read everything! So it’s really not a great feature for kids.