The Missing Letter

Sasha and Alyosha are blood brothers, and not just blood brothers, but twins. Each of them is exactly seven years, eight months, and nine days old, and they look very much alike. All summer, wearing their school uniforms, the twins... admired their reflection in the mirror and thought about how soon, very soon, they would start a new life. But they had no idea what adventures awaited them. It all started right after the first of September, when Sasha and Alyosha went to school for the first time. Now they had to wake up early in the mornings, pack their backpacks, and do their homework.
And if they somehow managed to cope with the first two tasks, the homework was a real disaster. Of course, try sitting still here when those pesky little sticks and hooks just won't turn into letters! It would be better if there were no letters at all! 
But as is known, wishes tend to come true... And Sasha and Alyosha suddenly find themselves in the magical Letter City, where, with their new friends, the brothers embark on a quest to find the missing letter, while the city's worst enemies - the letter-eaters - threaten to swallow the entire alphabet. "The Missing Letter" by Mikhail Raskatov is a classic for young readers, illustrated by artist Evgeny Medvedev.
For younger school age.