We speak to our children from the moment they're born (and often before!) In those early months especially, we know they don't understand what we're saying. Yet we still do it, because we know they will eventually get it. Basically, lots of information is absorbed before it gets expressed.
Over the course of our children's early years, we naturally support their language learning by breaking language down in many ways. For example, if your child points to an apple in a bowl, you might respond, "Oh, would you like an apple?" On another day, when you see an apple in a picture book you might say, "There's an apple." Go apple picking and you give your child yet another experience of "apple." You get the idea. We participate in our child's language learning by immersing them in their world through many, many language experiences.
Music learning works very much the same way. When we express ourselves musically and immerse our children in rich, vibrant music experiences where they can see and hear their most important grown-ups singing and dancing, then we are providing them with what they need to de-code music over time. They take in all that beautiful information over and over again (repetition is good!) and eventually they begin to express themselves. A single note "sung" on a "baaaaaa" will, over time, become a whole song. Just as a child's first uttering of the word "apple" starts with a simple "aaaaa."
Learning to sing in tune and march to the beat doesn't happen overnight — 3 to 7 years on average in western cultures — and through our shared experiences in the classroom and your continued music making at home, your child will eventually emerge as a confident music-maker. It's worth the wait.