Light Yagami/Harry Potter
Light was sure school books for four year olds weren't supposed to have words. More associations to go along with images, words and colors. Not all these. Light knew what Sayu learned during her pre-KG age. It sure wasn't this.
"Diddykins," Light said calmly to his obese cousin sitting obediently to his front. "You're too young to learn this stuff."
Dudley pouted. "Everyone knows some in class."
"You are not everyone," Light pointed out. "Remember how many tries it took to speak properly?" Dudley nodded. The younger kid remembered it very clearly. Once Light taught Dudley a word, he either had to use it clearly or get ignored. Light had no patience to listen to the inane babbles of an infant in their learning age. Baby Sayu was enough for once. Baby Dudley was the second. Twice, Light could not tolerate. He was neither a Saint nor had the patience of one.
Dudley was okay with it. He was the best well-spoken gentleman in the neighborhood, especially since Light still hadn't deigned to speak much in front of others, and Dudley enjoyed the praise and attention it brought him. He still was the best spoken student in his class. Dudley just wasn't the best in learning anything else.