>>> Any good drills to correct bat lag? My 8 yr old rotates his upper body too much or too soon and thus the bat is lagging behind. <<<
Hi Chris
I would suggest that what is causing your 8 yr old's bat lag is not due his rotating his upper body too much or to soon. His problem is that the angular acceleration of his bat is not staying in sync with the rotation of his shoulders. Therefore, his upper body fully rotates but his bat is left lagging far from contact.
Below are a couple of posts from the Archives that addresses this issue.
Swinging Late
Best hit balls pulled
Jack Mankin