Here is one of my favorite baseball training drills since it is great for all ages and levels of experience.   It keeps skills sharp, is fast paced and the kids have fun with it.
Hitting and Fielding Drill
To keep the drill organized, safe, and productive call out the number of the tee that you want the player to hit from.   This way the hitters only hit when you tell them to, there is only one ball in play at a time, and the hitters have time to put another ball on the tee.

Using three tees, put one at home plate (Tee #1), one on the edge of the outfield grass (Tee #2), and one in the outfield (Tee #3).

Each batter will hit 5 balls from each tee to players in the field, concentrating on one concept or principle at each tee, i.e. proper hitting stance, posture, touch step, opposite field hitting, etc., and then rotate to the next tee.

After hitting 15 balls total, the hitter becomes a fielder.

Vary the height of each tee to simulate pitches in different spots in the strike zone.

Players in the field are to call for each ball they intend to field (grounders too) to improve communication while playing the field in games.

For younger fielders have them rotate where they are playing so they can experience fielding on the dirt in the infield as well as the grass in the outfield.