Parents must lead by example!
Also, for kids ages 6-9, it's all about making it fun and playing games that help reinforce many movement patterns. It's not the technique that matters at this age, but that they have fun doing it.
Technique begins coming into effect beginning at 10-13 years of age. Training still has to be fun, but form begins to matter more.
It truly matters when they are 14-18 years of age. Form is very important at this age (and not excessive loading).
Speaking of loading, it can begin as early as possible (provided the child is ready) with simple things like bodyweight exercises, med ball exercises and light dumbbell and bar work to practice correct technique.
This is just some of what I've learned as a Level 1 certified Youth Fitness Specialist through the International Youth Conditioning Association (IYCA) - www.iyca.org. As I have an interest in opening a youth fitness facility in the future.