The most difficult thing with 6u is practice. They have an extremely short attention span. I'd play all kind of games that incorporated at list one skill.
I had trouble getting the girls to swing through the ball, so we had a home run derby one practice. We made an arcing line inside the baseline and they got a home run for every ball hit over the line in the air. The parents really helped by making it a big deal and cheering. (I didn't ask, but it was good)
Take breaks during practice. It's not about how long you practice, it's how much did they pay attention to.
I had trouble getting the girls to swing through the ball, so we had a home run derby one practice. We made an arcing line inside the baseline and they got a home run for every ball hit over the line in the air. The parents really helped by making it a big deal and cheering. (I didn't ask, but it was good)
Take breaks during practice. It's not about how long you practice, it's how much did they pay attention to.