React: Mapping children of a parent component

To wrap your children into a wrapper just put the call to React.Children.map into the wrapper component:

const OpaqueWrapper = ({ children }) => (
    // check that children is defined 
    // if you do not want your wrapper to be rendered empty
    children && (
        <Wrapper>
            {React.Children.map(children, child => (
                React.cloneElement(child, {style: {...child.props.style, opacity: 0.5}})
            ))}
        </Wrapper>
    )
);

Also note that you have to merge the styles provided to the original child with the styles injected or you will lose the ability to style the children at all.

See this codesandbox for a working example.

As to why it did not work in your code: Are you sure that your <Card> component does handle the style prop correctly, i.e. applying it to it’s children?

EDIT:

The sloution wraps all children components in a single wrapper, but I
would like to wrap each child with the applied wrapper , as shown in
my question.

The just move the wrapper into React.Children.map:

const OpaqueWrapper = ({ children }) => (        
    React.Children.map(children, child => (
       <Wrapper>
           {React.cloneElement(child, {style: {...child.props.style, opacity: 0.5}})}
       </Wrapper>
    )))
);