The first two questions I hear most often from parents of young children is, "Is my child ready to take lessons?" and "When can my child begin lessons?" It makes perfect sense for parents to ask this question, and I'm glad they do!
There is no set answer to the question about whether a child is ready to take lessons, but I like to answer the question this way: "When your child is ready is the best time to begin." Every child is different and every child learns differently and at different ages, so that's the best answer I can give.
Personally, I don't like to take on students younger than 5 years old, but some teachers do. Finger independence and knowledge of the alphabet are pretty important for a beginning piano student. But like I said, some teachers do design their teaching programs specifically for kids younger than grade school. I will give a big plug here for Kindermusik as a great starting place for very young children who appear to be interested in music.
There is so much information on the Internet about how starting piano lessons early helps brain development in the young child, and research proves it to be so. That doesn't mean that if a preschooler walks up to a piano and starts plunking down on the keys he should be signed up for piano lessons. If you have a child who appears to show an interest in learning a musical instrument and it is feasible for that child to actually be able to play that instrument, begin your research for a teacher. Make sure the prospective teacher meets with you and your child for a consultation before agreeing to pay for lessons.
I, like many other teachers, use book-based method teaching resources, so I always check to make sure a young student has good reading and understanding skills. If not, a parent needs to understand that if she wants her child to progress then she needs to be heavily involved in the process . . . and practice. That kind of involvement includes sitting with the child at practice sessions. Parents need to be fully aware that in order for their child to feel successful at learning they will need to make a commitment to their involvement.
Attention span is another consideration with the very young starting music lessons. At the initial consultation, expectations from both the parent and the teacher need to be openly discussed. A teacher may ask about the child’s classroom experience in school. Can the child sit still during reading time or during project time? It's critical that a private music instructor knows about a young child's attention span, as teaching plans may need to be altered to involve more activity during the lesson time.
Again, I think the most important thing to remember is that the best time for a young child to begin lessons is when that child is ready. An informative discussion involving the parent(s), teacher and child is the key to making a decision.