Up to 80% of the words in your children's books are considered 'sight words'. If a beginning reader is able to memorize the sight words, they will be more able to concentrate on the meaning of the text instead of having to struggle with every word in the book. A lot of the words in this list have unusual spelling patterns so it is not easy to sound out the letters, and most of the words are hard to describe with a picture. Memorizing these patterns will give students a great start when learning to read.
Dr. Edward William Dolch studied the most commonly occurring words in the children's books of the 1930s-40s. He created a list of 315 words (220 'service words' and 95 'high frequency nouns'). The Dolch words are usually split into groups for each grade level from pre-kindergarten to third grade.
Playing games is important for a child's development. The only way to master a skill is with repeated practice, and turning this repetition into a game is one of the best ways for children (and adults!) to stay interested.