Electronic keyboards are either touch sensitive of not. NOT = cheaper. BUT if it isn't touch sensitive, then they won't understand the difference between pianissimo and fortissimo (soft and loud).
You'll spend much more money on a touch sensitive keyboard. 15 years ago, when DH bought my keyboard, it was a HUGE difference- like $150 vs $600-$800. Not sure of the difference now.
My kids all took a beginning class this past summer. The keyboards used in clase are not touch sensitive. Although the music is noted with "p" and "f", she didn't talk about it. She was most concerned with them understanding notes, finger placement, and rhythm.
We have both a piano and a keyboard now. Keep in mind that your child will play with all the bells and whistles. You should let him get it out of his system, but insist that he use the piano setting for practice.
I also recommend getting a stand made for keyboards; I think they are adjustable. In class, the tables are so high, my kids actually have better hand position when standing. At home we have the keyboard on a TV tray and use a folding chair. It's OK, but not the best.