As someone that walked that path, a few suggestions:
- If I was to start today, it would definitely be on a button accordion (C key mapping), not piano.
- Classical music? Free Bass is a definite must. TONS of piano music is out there... and for that you NEED a Free Bass instrument.
- kids learn fast... besides, if the pattern for the Free Bass (which they MUST learn anyway) is the same as the right hand, its a 2-for-1 win!
- If they are bright and motivated... regular classes, likely at a conservatory or proven high level competent teacher is a must.
Now... my parents pushed way too hard, too fast and I burned out and stopped playing for 37 years. Excellent if you want a child prodigy... that plays until adolescence and stops there, possibly forever.
If you do not want that, be supportive, do NOT push too hard. Interest will wax and wain. During periods where interest falls, encourage and motivate, but understand that most kids will tend to want to stop after a few years. If you can gently nudge them over the hump (and this will happen SEVERAL times), they will regain momentum and continue to advance.
Don't push too hard.
The ability to read music is VERY important, but once a certain level of competence is reached, the next level is performance without musical notation. Kids have amazing memories. At my peak, I had easily 300-500 pieces of music I could play by heart and with minimal effort in terms of playing to retain. Encourage musical accuracy, but also encourage improvisation, both are important tools of the trade in the musical world, and to be honest, not many can do both without lots of practice. I myself find improvisation difficult, but am working on it.
Most importantly, define goals, provide the best teachers you can, give them breathing room and rest time, but understand that the more regular the practice sessions are, the faster the advancements come.
Also, in terms of instruments, understand that there will be more than one, if you play this game long enough. Quality instruments are going to be expensive no matter what you play, but going for conservatory level instruments is a notch higher on the pricelist. Be ready to invest, if serious... but start with a used instrument, if you can find one.
Playing alone, but playing with others... SUPER fun and highly encouraged. Not only do they learn how to play with others, but they will see and learn from others and see different styles and it also becomes a bit of a social event for them, and that is always fun... and the more we can make anything fun, they longer they will stay with it.
That's my 2 cents.
