I would describe the Nightcrawler and Mystique mother-son relationship as estranged. This is because as Nightcrawler was growing up, he did not grow up with Mystique as his mother. Moreover, from the time they meet and realize that they are on different sides of the teams, they do not connect.
It's kind of weird. She claims to be his mother but as far as I know it's never been proven. If she is the mother, she left him with a band of gypsies who raised him. After some townspeople thought him a demon he fled to a monetary where he was taken in.