Enid Blyton 
The Mystery of the Secret Room [EPUB ebook] 

Pip set out his painting things, poked the playroom fire, and sat down to finish his Christmas cards.
“You do them nicely, Pip, ” said Bets, looking over his shoulder. “I wish I could keep inside the lines like you do.”
“You’re only little yet, ” said Pip, beginning to paint red berries on his card.
“Well, I’ve had another birthday, and I’m nine now, ” said Bets. “I’m getting bigger. You’re still twelve, Pip, so I’m only three years behind you now.”
“When are the things coming?” asked Pip, looking at the clock. “I told them to come early. It’s fun to do our Christmas presents together.”
Bets went to the window of their big playroom. “Here come Larry and Daisy, ” she said. “Oh, Pip, isn’t it fun to be altogether again?”
Bets didn’t go to boarding-school as the others did, and she often felt lonely in term-time, when her brother Pip was away, and their three friends, Larry and Daisy Daykin, and Fatty Trotteville.