Disclaimer: I own nothing you recognize from the Harry Potter universe.
One morning in mid-April, Xenophilius walked into Luna's room to find the little girl sitting up in her bed waggling her left top front tooth back and forth. "Look, Daddy!" she said. "I have a looth tooth."
"I can see that, moonbeam," her father replied. "It won't be long before a Densifae comes."
"What'th a Denthifae?" asked Luna.
"Well, Luna, they're similar to a creature the Muggles call a tooth fairy," Xeno explained. "But they do not leave money in place of teeth. Instead, they simply collect teeth and transform them into baby Densifaes."
"Will I get to thee one?"
"Probably not; they usually keep themselves well hidden from humans," Xeno told her as they headed down to the kitchen for breakfast.
Pandora, who had been busily cooking, turned around with a smile when she heard Xenophilius and Luna approaching. "Good morning, Lu-Lu," she said. "Did you sleep well?"
Luna nodded. "Gueth what, Mummy? My tooth ith wiggly!" She showed her mother the said tooth, earning a gasp from her mother.
"You really are growing up," Pandora said fondly.
"Mummy, ith it all right if I juth have eggth for breakfath? I don't want my tooth to come out juth yet 'coth I wanna thow it to Ginny."
"Understood," her mother said as she put some eggs on Luna's plate.
As Luna sat on the sofa later that morning awaiting Ginny's arrival for their play date, she swung her feet back and forth while repeatedly poking her loose tooth with her tongue.
The redhead emerged from the fireplace with her mother at 11:00; Luna rushed over and said, "Hi, Ginny!"
"Hi, Luna!"
"Be a good girl, Ginny," Molly told her daughter. "I'll come back for you in a few hours." After she left, Ginny stared intently at Luna.
"Why are you making those weird faces?" she asked.
"Becoth I have a looth tooth," Luna replied, opening her mouth wide. "Thee?"
"Wow," said Ginny in awe. "I can't wait till I start losing my baby teeth."
"Daddy sayth when my tooth cometh out, a Denthifae will come and get it."
"What's a Densifae?"
"They're fairy-like thingth that collect teeth and turn them into baby Denthifaes."
"Oooooh!"
"Wanna go play with Newt?" asked Luna.
"Yeah!" Ginny replied; the two girls headed up to Luna's room where Newt was playing with a ball of yarn.
That night as Luna was tucking into that night's pudding, chocolate pie, she suddenly found her tooth in her hand. "Mummy, Daddy, look! My tooth came out! And it's covered in chocolate too! The Densifaes are gonna love it!"
"They certainly will," Pandora told her. The five-year-old quickly finished her pie before running to her room to place her tooth on her nightstand. she lay in bed that night poking her tongue through the gap in her teeth and imagining what the Densifaes' reaction might be when they saw her chocolate-covered tooth, until her mother came in to read her a bedtime story.