Children's key is missing

**Issue:** There is something wrong with children's key.
**Example:** The expected output should be
```

```
But I got an output without `RadioButton's` key:
```

```
I am sure the radio button element is correct:
```
{ '$$typeof': Symbol(react.element),
type: [Function: RadioButton],
key: '1-1-0',
ref: null,
props:
{ label: 'auto',
tabIndex: '0',
disabled: false,
checked: false,
name: '1-1' },
_owner: null,
_store: {} }
```

Any suggestions about this?

Reproduce the supplied ReactElement-to-JSX example and trace how child React elements are serialized; the issue names no source file or test to start from. Done means the generated JSX includes key="1-1-0" on the RadioButton while preserving the shown props and parent key.

Written by the indexing model from the issue text.