Scorpius Malfoy is not his father.
For one thing, his father would not have done anything he had not planned to do. There are many speculations even eleven years after the war about his involvement in it and his father has been quite tightlipped about it all himself, but Scorpius knows that while he may have been forced to do many things, he had done them.
Another thing he thinks his father would not have done is fall in love -stupidly, in a head over feet manner, without consideration for propriety and the like- with his greatest rival.
All he knows is that when he sees the Sorting Hat proclaim her a Gryffindor he is a goner at eleven and he doesn't understand why.
He doesn't understand even when he is amazed by her tenacity, her sheer brilliance that keeps her at the top of the class no matter what.
Doesn't even realize it until he's fourteen and she cheerfully turns his notebook into a thimble -and messes up his tightly controlled script- and back into a notebook without blinking in Transfiguration Class.
At least, he doesn't, until Professor McGonagall gently chides him for staring.
Rose Weasley is not her mother. Or her father, even though her red hair and her last name certainly comes from him.
For one thing, her mother and father both found someone right for them over many years through a friendship -filled with moments of non-friendship, as her mother tactfully said and her father looking incredulously at her from afar saying "non-friendship being those birds you sent at me?- that grew over time, matured, became love.
Her mother and father would have never fallen like this, without consideration, without thought, just because one day she looked up and saw his gray eyes from across the Great Hall looking steadily at her.
She blames her father for actually making her aware of him; if he hadn't pointed Scorpius out he would have been another face in the crowd, though admittedly she would have probably heard of him from his grades which were close to hers in excellence.
It's easier to blame her father for this, this sudden realization that there can be someone who just fits, fits well, even though you're still starting to know about him -mostly from Albus, sunny and cheerful where Rose is contemplative, who doesn't feel the need to censor how Scorpius isn't at all like any tales Uncle Ron has said of his father.
It's easier not to think about how what she hadn't expected had suddenly presented itself just because a pale boy with gray eyes had looked at her steadily where his heritage had previously demanded he look away with a sneer once he even caught sight of someone like her.
Their thoughts are the same as she returns his gaze as steadily as she can, her hands trembling underneath the Gryffindor Table and his hands slightly sweaty.