Teach them to play, not to fight for now. Best thing you can do with young kids is teach them some playful judo/bjj/grappling. Kids love to wrestle and roll about anyway, so just get them used to doing them right.
Striking isn't much use to teach children, especially cause of how they can damage themselves from striking.
So instead maybe have them practice playing sorta striking tag, where they have to practice dodging and slipping the other kids hands when they try to "tag them".
Forget the techniques or forms, just lay a nice solid base for learning or using skills and techniques once they're old enough to learn them.
That is good advice for the young children! Teaches agility and good body control which will be useful later in their training. Of course that needs to be tempered with the fundamentals of the respective art or they could be gaining bad habits that will later need to be undone.