My younger daughter turned thirteen today. Yeesh, I now have two teenaged girls *shudders*.
My oldest wrote her a Portal/Star Trek: The Next Generation crossover fic as a present (at the end, she wrote Congratulations on turning old). My six-year-old thoughtfully wrapped up one of his own toys, a toy knight and horse, for a birthday present for her. When she opened it, he informed her, "I never use it, and anyway, one of the dogs chewed a hoof off."
She laughed, and graciously thanked him anyway:-).