Standard(or best looking) SFINAE implementation for stream opearator overload

Question

I have the following code

template<typename S, typename T, bool h = is_class< decltype(T::children)>::value >
    S& operator<<(S& s, const T& t )
{
    return s;
}

that will overload the operator<< when a class have a member variable named children.

What is the standard way or do there exist a better looking way for making the function fail when is_class< decltype(T::children)> fails.

I cannot use the return type or an argument because this is operator overloading.