When teaching baseball or any other sport regardless of age, the players in ability to understand what the coach is trying to express is sole responsibility of the coach. Teaching involves respect, clarity, organization, motivation and context.
People learn by example, Coaches who are respectful of children are not just modeling a skill or behavior, they are meeting the emotional needs of those children, and create the conditions for children to respond whole heartedly.
Clarity, to effectively communicate using clear ideas, clear goals, clear questions and clear conclusions. This level of interaction is truly age dependant but as a coach you must identify and speak to each players level of clarity. Relate to the age and reference level of your players.
Coaches are not teachers replete with pedagogy that work for every player. Granted, in the High School ranks and beyond this changes, but the majority of players do so through the recreational leagues where Dads, Moms, Uncles, Aunts and Grandparents of all backgrounds volunteer for the joy and frustration of being the coach.
Be prepared for practice with written notes and time schedule. Organization is...