Live BP is great... but it is not efficient use of team practice time... And when my DDs are throwing live BP, the coach tells them... "throw it down the middle, we need them to hit..." <facepalm>
There are no easy answers, especially if the pitcher is significantly faster than what your hitters typically see, and you are talking 12U. What I notice first when hitters are overmatched is that they speed up their swings and then start to anticipate rather than react, which is understandable. The go-no go decision to swing the bat is largely subconscious and based on previous experience, getting that experience is difficult. Rather than live BP I prefer at-bats, it benefits the pitchers and hitters.