C++ ::  Getting Error With List Of Key Type

I have a Polymorphic class and some child classes, of which I need to make multiple instances of, using a list container. I've set the key type to be a unique pointer of the polymorphic class, and the values of each element pointing to a New Child instance, like so:

std::list<std::unique_ptr<Polymorphic>> polymorphic;
polymorphic.push_back(new Child(foo, bar));

The only problem is that when I try to push_back a new element, I get a compiler error, saying "No instance of overloaded function".Should I try and create a pointer object on it's own and push back that object as an element, it will work fine:

std::unique_ptr<Polymorphic> polym(new Child(foo, bar));
std::list<std::unique_ptr<Polymorphic>> polymorphic;
polymorphic.push_back(polym);

Is there some way I can push a new Child instead of having to create a Polymorphic pointer object and pushing that?