Two totally different languages with two totally different use cases. Their use cases should not overlap if applied correctly.
C++ is a very high level language compared to C. C++ has low level constructs which closely resemble C but should only be used for high performance implementations of high level abstractions.
You are right, it is crucial to emphasize to beginners that these languages are different (and C++ not being some kind of add-on to C, which is - considering its name - a valid guess, but we have the same discussion with Java and JavaScript). But I think learning C, Python and JavaScript (and maybe some Java) to a degree that let's you get useful work done, is a lot simpler (meaning takes less time) than learning C++.
Not that I would discourage anyone from learning C++ (ok, probably, I might) I just consider it a bad PL for people starting out with programming.
Not only that, but Cython really takes away a huge amount of performance bottleneck encountered in Python code by generating pure C from a Python language superset.
C++ is a very high level language compared to C. C++ has low level constructs which closely resemble C but should only be used for high performance implementations of high level abstractions.