Light Yagami/Harry Potter
So when Light talked to Dudley at his third birthday party, in front of everyone and even offered him cake, Dudley was pleased. Pleased as punch, proud as a peacock and all evening, the child stole looks at his cousin as if to check whether he still had his approval.
Children. How easy to train them.
Light was sure that Petunia knew at some level something was going on. She didn't know what, wasn't sure even what a two (soon to be three) year old could do. But she was a mother and she had seen the subtle changes Light had been influencing in Dudley.
It was too late though. Light was firmly entrenched in Dudley's heart as 'favorite human'. His favor rated even higher to darling Diddykins than that of his own father. Any changes to that status quo would require more knowledge about human behavior than the Dursley couple possessed and a firmer hand than either of the pair was capable of raising to their own flesh and blood.
Light was glad he hadn't outright killed Vernon and Petunia all those months ago. Turning the son onto the parents was much more fun. And when they grow older, if the couple still hadn't changed their tune and continued to abuse Light, then Light would turn the son into his parent's conscience too.
Dudley calling the CPS because he thought what his father and mother were doing to his cousin was wrong. If that happened, then Light would surely relish the expression on Vernon and Petunia's face.