Are the viewers who donate so much on Twitch Streams all rich?

Some donate hundreds of euro.

Are they rich or do they just spend all their pocket money on it?

Ever heard of "working"? If you are a good computer scientist or industrial engineer, or whatever, you can afford that…

Adults certainly don't watch Twitch streamers that make children's content. As an iGeNiEuR, you also have to pay rent, pay off the car, pay for private health insurance and finance the son's student exchange.

Private health insurance, finance the son's student exchange

Not everyone has private health insurance or a child. There's also enough content that isn't just for kids. I think rather that you are the rich man here, or your parents.

Adults certainly don't watch Twitch streamers that make children's content.

Of course they do. How do you know it isn't?