Peter and Lucy have always seemed to have an adorable relationship, and I wanted to write some things that demonstrated that. I placed him at around sixteen and her at eight, so that's where the title comes from.
*Updated* A lovely person pointed out to me that C.S. Lewis placed them at 8 and 13 so I decided to change it. It's different now. Thanks!
Peter sighed. Three months ago, everything had been perfect; they'd been a close, loving family without a care in the world more trivial than final exams and what to have for lunch. And now…now he and his siblings were on a train, speeding far away from the only home they'd ever know. If they were lucky, it would still be standing when they returned to it.
He surveyed their train compartment. Susan and Edmund had both lapsed into sleep, perhaps out of lack of anything better to do. Peter assumed that Lucy had also, as she was leaning against the window and hadn't made a sound for quite some time. But as he watched her, he realized that her shoulders were shaking ever so slightly, and she was sniffling quietly to herself.
"Lucy…" he whispered quietly, gently placing his hand on her shoulder. She turned to him, a pitiful expression mingling with the tears on her face. "What's wrong?" he asked, though he already knew.
In answer, his youngest sister flung herself on him and sobbed into his chest. He stroked her hair, a little taken aback by the vehemence of her emotions.
"What are you thinking about, Lu?" he asked quietly when her snobs had turned to sniffles.
"I miss mummy," she said after a minute, rubbing her eyes. Peter nodded supportively.
"What if the Professor's mean?" she asked a few moments later, turning to look at Peter worriedly.
"He won't be."
"Yeah, but what if he is?"
"Lucy, I promise, I'll keep you away from him. But he won't be mean," said Peter, resisting the urge to smile. Lucy nodded, but she still had the little crinkle in her forehead that she got when she was worrying about something.
"Let's do something to take your mind off it, hm?" said Peter.
"Like what?" asked Lucy, sitting up. Peter glanced around, searching for something to distract his sister. He hadn't really thought his plan out all the way when he'd offered it to her. After a second, Peter's hand brushed against the book he'd been reading. Though it might have been a bit advanced for her, Peter figured she'd enjoy it enough.
"Here, I'll read to you, alright?" he said. She nodded excitedly, and crawled all the way into his lap, snuggling into the crook of his arm as Peter cleared his throat and began to read aloud. Lucy had always sworn, since she was a tiny girl, that Peter read stories the best of anyone. Edmund simply refused, of course, and Susan was too prim and proper to do the funny voices and act out Lucy's favorite bits; but Peter always had, and Lucy loved it.
Peter glanced over at his baby sister some time later to discover that she'd peacefully dozed off with her head on his shoulder. He smiled to himself, and kissed her forehead, before going back to reading to himself.