Have you consider using the new React Fragments? (in v16)
This would be the simplest solution as it would by pass the whole array/key issue.
If you need to pass key, then I’d suggest to simply require the components to have the keys. This is how React works, so I wouldn’t suggest you to hide this behavior behind an interface that might not be predictable.
If you really need to do this, then you can use React.cloneElement to clone the element and inject new properties:
React.cloneElement(element, { key: 'foo' });