"У ребёнка всё хорошо."

Translation: The child is fine.

[GabrielBer689099]

WHY WE USE Y HERE

[TEETUS1]

Think: "To the child: everything is good"

[alisakriv]

What's wrong with the child is good?

[GabrielBer689099]

this kinda structures are so confusing

[Shady_arc]

It is a set expression. If you ask "как у тебя дела?" (lit. "How are things you do?"), you get "У меня всё хорошо" (the "stuff" I do is fine)—of course, if the answer is optimistic at all. ^_^

It works the same for anyone else.

[Wayne_19920]

"The child is doing fine" was not accepted.
The suggested translation of "the child is fine" is a little ambiguous in its meaning. Is the the child safe and well cared for or is the person tasked with watching the child pleased that the child is we behaved and not causing problems? Or could it be both as in english?

[Shady_arc]

I think it is perfectly OK. Added your translation to other options.