Reading requires two skills, decoding and comprehension. A child needs to be able to figure out what the word is (decoding) and what it means (comprehension). For example, you can sound out (or decode) the word "fresas" but if you don't know Spanish you may not know that it means "strawberries" (comprehension). Kids need both skills to be successful readers.

Twinkle Twinkle Little Star is also a good example of how singing helps with comprehension. Language is made of common words, ones we say frequently, and rare words, ones that don't often occur in daily conversation. Most children easily learn the common words, but not all children are exposed to the same amount of rare words. How often do you use the word, "twinkle" in daily conversation? A child who never sang Twinkle Twinkle Little Star might not know the word "twinkle" when they start kindergarten, but any child who has sung the song, will. Think of other common children's songs. What rare words do you find?
So that is why we sing every week in Story Time. We want kids to learn decoding and comprehension skills. We encourage parents to sing with their children as well. It doesn't really matter if you have a good voice, or even if you can carry a tune. The more we sing with small children, the better prepared they will be to become good readers.