✔ 最佳答案
I have played piano for more than 25 years, I never think of buying a digital piano to substitute a piano. They are two different types of musical instruments.
With a digital piano, you can do a lot of musical modification, for instance, change the key, change the sound, synthesize music (combine sound various musical instruments together), control volume output (or even use headphone), etc. But with a piano, you can only play it like a piano. However, the sound (whether thick or thin, staccato or legato) variation from a piano is greater and so people cannot use a digital piano to play classical music.
The touching and sound of a digital piano are very different, although the touching of a much expensive digital piano is more like a piano, they are still different. Usually a digital piano is softer than a piano, and, the range of loudness of piano is greater than digital piano, that is, the volume range of piano is greater.
If you decided to let him learn piano, I suggest you should rent a piano because it is a good start for experiencing playing piano. However, I don't have experience for renting a piano.