Meet Caroline. She's 2 1/2 and loves to practice. So, I made her a practice book and she LOVES it! She's my only child that begs me to practice....3 or 4 or 5 times a day. She can successfully play every variation of twinkle on open E string, including variation B if someone is playing with her. She has okay posture and a baby bow hold - very tight - but she's working on a round thumb and pinky.
What she can't get yet...everything else. I try even a simple play position and rest position feet game. It's like I'm speaking Chinese to her. She doesn't get it. But she still loves to play.