When Jason was just a toddler, Thalia always used to tuck him in. And then there was a time when nightmares came haunting his every sleep. He slept less and less, making him paler and paler. So in order to soothe him to sleep, Thalia would always sing a lullaby for him. Well, more exactly, humming. She would sit by his bed, hold his hand and pat his head gently, humming his favorite song – Twinkle Twinkle Little Star. And with that, he wouldn't be scared of nightmares or monsters under his bed anymore. Sometimes, at camp, or even at war, he could still hear the humming sound when he closed his eyes. Even though he didn't understand why due to his memory loss, he found himself enjoy the sound of it.
To Annabeth, Thalia is and always will be her best friend, her model and big sister. During their run, she always huddled with Thalia whenever she was not on guard. Because only with Thalia's soothing could she sleep. Annabeth was also a victim of nightmares, and worse, spiders. When nightmares came, Thalia would put Annie's (as she used to call) head on her lap, run her gentle hand through Annabeth's hair and hum the oh so familiar song, Twinkle Twinkle Little Star. Thalia said she had the habit of humming that song, sometimes unconsciously. Annabeth kept wondering why she got that weird habit, but didn't press seeing Thalia's expression after she had asked. Months after that fateful day, she still hummed herself the song to chase the nightmares of Thalia's death away.
After Jason got married, sometimes when he had nightmares about the Giant War, he would make Piper hum the song for him. Just like in the old days.
After Annabeth had kids, she would hum the song for them every night, and sometimes, tell them the stories of the girl who used to be a tree.
They still remembered.