when i was in school the 4th graders all played Tonettes, which were
small plastic flutes, like recorders. this apparently was determined
by the school system at the time to be a good instrument to start out on.
The piano, it is true, is quite linear, and a good way to see the relationships, intervals, etc. but is large, heavy, cumbersome and
too expensive for some . Many kids start out on violin, with the
Suzuki method before they are 5 years old. This seems to be quite a good way...Suzuki explains music as a language, and the younger you are when you learn it the better you can learn. Both my kids were Suzuki students and i believe it gave them a great understanding and appreciation for music.