Occasionally, I am contacted by a parent who wants to start their 2nd or 3rd grader (I've even heard younger!) on clarinet or saxophone. My standard age for admittance into the studio is 4th grade and preferably 5th grade. While I think it's fun that a younger child is interested in playing a woodwind instrument, I will very rarely accept a 3rd grader into my studio; even then it's only after a series of questions and discussions with the parent over the course of a couple weeks. "But they're so jazzed about it!" Yes, and I'm jazzed that they want to play an instrument, but there are some things to take into consideration when we mix children and instruments.
Interest - It's not just the initial "I want to play an instrument" that matters. Does your child have a level of interest high enough to motivate him through the first several hurdles of learning to play? When the going gets tough, will he work through the frustration or put the instrument down? If he's not accepted into a studio and asked to wait a year or two, what is your reaction? Why is it so important for him to start right now? If there really is a high level of interest there, telling the child that they can do it, but they'll have to wait until they grow a little more shouldn't be a big deal. In the meantime, playing a more age-appropriate instrument is a good option. (More on that later.)
Size & Motor Skills - Seriously, I've had 6th graders who were small enough that handling a saxophone was difficult. Imagine a 2nd grader! Sometimes, the instrument is just plain too big for small bodies and especially for small hands. There are instruments out there that are sized down for smaller builds, but again, why not just wait another year or two and you can start playing the real thing? In the meantime, while little bodies and little hands are growing and getting stronger, let's work on skills to prep them for playing woodwinds. Younger children often don't have the detailed fine motor skills and/or coordination needed for woodwinds, but there are plenty of activities to do that will build on these while you're waiting: simple sewing like plastic canvas and cross-stitch; knit or crochet; braiding or knotting friendship bracelets; painting and drawing; playing games like "Pick-Up Sticks" or "Jenga"; origami and other paper crafts; the list goes on. With crafting items, a side benefit is the child learning to follow instructions and patterns carefully. And of course, you can have the child play an instrument well-suited for younger ages.
Bone & Tooth Development - Here's one of my biggest hangups to allowing children under the age of 9 to play a reed instrument: their bones and teeth aren't fully developed yet. The force exerted by the muscles in the lips and yes, the jaw too, is considerable. I'm not willing to risk altering a child's natural oral dimensions by working with them before their bones and teeth are substantially set. And then there's the obvious: can you imagine trying to play clarinet with a missing tooth in the embouchure?? Ouch! Even if it's not painful, it's going to be very difficult, so we'll have to put the instrument down until the permanent tooth grows in. Then we could start again... until the next tooth falls out! Bone development in the hands (particularly the right hand) is an issue, but there are ways to work around it. There's no working around the need to set an embouchure around the mouthpiece to make a sound.
So, what do you do while you're waiting? There are lots of activities that promote the physical skills needed to play an instrument, and lots of games that emphasize necessary elements of music. For maintaining interest, take your child to live performances so she can see and hear real-life people making music right in front of her. These performances don't have to be limited to full-blown symphony orchestras, either. Check local university calendars for faculty and student recitals (which are typically free admission - bonus!!).
And if your child really, really wants to play an instrument, go ahead and get started on one. Piano is classic for reading skills and movement of fingers, and it's super-easy to make a sound - press the key and the note comes out! Violin is a little more challenging to start than piano, but is a good choice for small hands. If you want a woodwind instrument, play recorder. "What, but that's just a toy!" No, it's an instrument, and for hundreds of years was the prevailing wind instrument, excellent for demonstrating technique and musicianship. It's now favored in elementary school classrooms for good reasons: students learn to manage their air to make a good sound, they can articulate notes, they must cover tone holes with their fingers (great preparation for clarinet!), and they must exhibit the same reading and rhythm skills as any other instrument. If your child wants to play a woodwind but a teacher counsels you to wait, this would be my avenue of choice.
Don't take it as offense if a qualified teacher says that your child isn't ready. As teachers, we care a great deal about our students. We want them to enjoy music and we want them to succeed, and we do what we think is best to set them up for a lifetime of playing an instrument, professionally or not. Be cautious of woodwind teachers who are quick to take any student without question - most qualified teachers I know are meticulously careful about shaping their students to the instrument, and it takes time and thought. We don't let dance students start out en pointe, we don't let tae kwon do students spar on their first day. Playing an instrument is both a mental AND physical process. If you're encouraged to wait, it may be best to wait. Remember that there are plenty of professional musicians out there who didn't start playing until 5th or 6th grade beginner band. Wait until your child is both mentally and physically ready, and watch how they'll make progress!