If You Give a Boy $5

If you give a boy $5, he's going to want to buy the alphabet. Literally.
When he gets the alphabet, he will spell all kinds of words. Then he will decide that three-letter words are too easy and will demand to spell words with blends, and compound words like watermelon. Seeing all the letters and spelling will rub off on the boy's brother.
The little brother will decide to spend his $5 on an alphabet book. When the little brother gets the alphabet book, he will carry it all around the house and ask you to read it to him at least three times a day. He might even sleep with it at nighttime. Reading the alphabet book will remind the big brother of his new letters. He'll probably ask to spell harder words and maybe even sentences. And chances are, if you let him write sentences, he'll want another $5 to buy a second set of letters.