They don't publish that on their websites, though.

Does X personally post ai generated kids to people's accounts or do people make pictures with a tool and post them on their own accounts?

X is not a person, it is a website run by Elon Musk.

Elon, through his company, publishes the photos. I don't think it matters whether he posted them or not. He was aware of and encouraging of the practice, at least when applied to photos of adults.

Legally, he does not. The poster publishes them onto their own page.

In the EU the platform becomes responsible for posted content, the moment someone notifies them that they are hosting something illegal. They have plausible deniability until notified, after which they have a certain time to act, and if they don't they are criminally liable. The user posting the content is also liable, from the moment they made the post.

Are lewd drawings illegal? To my knowledge unless they are real photographs then it is legally fine, if disgusting.