Reference to vector of parent or child

  c++, inheritance, stdvector

I have recently created a class inheriting from another preexisiting one

class Child: public Parent{

and another class that contains a reference to a vector of parents

// foo.h
class Foo{
    std::vector<Parent>& things;
    Foo(std::vector<Parent>& things);
    // + a bunch of other member functions

The members are implemented in a separate file

// foo.cpp
Foo::Foo(std::vector<parent>& things):things(things){}
// ... other member functions of Foo 

I want to make Foo work with vectors of typestd::vector<Child> as well.

I am aware I could make Foo a template

template<class c>
class Foo{

and add the following lines to the end of foo.cpp to avoid linker errors

template class Foo<Parent>;
template class Foo<Child>;

This is not ideal because in the future Child likely not going to remain the only class inheriting from Parent and touching Foo.cpp every time a child of Parent is born seems not like an elegant solution to me.
Is there a better way, than making Foo a template?

Source: Windows Questions C++