How do you define "lessons"? I have three children ages 5, 3, and 22 months and all three of them are playing the piano at various levels, all of them are learning musically, but none of them are currently taking formal "lessons". I believe that a parent (or a good teacher) can teach children of ALL ages to be involved with the piano. At the very least, children should be involved in some type of music creativity. They might surprise you at what they can do with just a little encouragement. Let me give you some examples from things I've done with my children:
- My youngest LOVES to sit with me at the piano and play along while I practice. You can see a picture of this on my profile picture :) This is a great way to form a closeness with your child while allowing them to become familiar with the geography of the piano and basics of how the piano works.
- I will often get my children together and let them pick a simple tune (ie "I've been working on the Railroad"). I will then let them take turns picking animals and I will play the tune so that it sounds like that animal (as best as I can) while the kids act out the part - they LOVE this game! It gives me the opportunity to practice improvisation and transposition, while the kids get to have fun and hear how music can affect our moods and can represent feelings/characters.
- I've already started my two oldest in learning Hanon. This provides fairly simple patterns that they can learn and practice to gain finger dexterity and familiarity with the piano. Beginning them in scales and chords is also quite simple. Just take it slow, be patient, and understand that all children go at their own pace.
- Sometimes I find a song that my kids like (a Disney song, or something on the radio) and then I'll teach them just a few notes of the chorus. As an example, I taught my three-year old son to play the opening notes to the theme from the Pixar movie, "Cars". He loves to play it :)
- I NEVER ask my children to stop playing the piano. If they hop on the bench (which they will randomly do throughout the day) then I let them just explore and play. Doing this, my daughter composed her first song a couple of weeks ago and entered into the national reflection's contest. You can hear a recording of her playing it here.
- I also often let my kids listen to recordings of great pianists playing short pieces of music and then ask the kids to talk about what they imagined while they listened. This is a great way to get their imaginations running and invites in creativity through music.
- Of course, there are also the formal sit-down lessons that I've done mostly with my oldest child. This is a great time to talk about chords, scales, dynamics, etc (in ways that children can understand). I think that even 10 minutes a week, with encouragement to practice (or "play") daily, will work wonders on a child.
So my official answer is, "It is NEVER too early to get your children involved with music/piano". As far as "formal" lessons - I guess that depends on how comfortable you are with getting them involved in your home, your financial situation, and the ability of the teacher. If you don't feel comfortable trying some of the ideas I've suggested above and you can afford lessons, then get your kids involved with a good teacher right away. Find somebody who can do some of the simple ideas I suggest, or that has lots of great ideas for kids that gets them involved and excited about the piano!
I hope that helps somebody!