Heaps, .get_smaller_child() method

Here in this exercise, as you can see below, I was wanted to create .get_smaller_child() method.
I created as I was requested in the instructors however I couldn’t understand the logic behind this specific code:
What is the purpose of comparing the index of right_child with self.count ? What is the relation of self.count in finding whether there is a right_child or not ?