Hi Mateo,

The best place to start is to get the kids used to holding the racket and developing their hand-eye coordination with the racket and ball.

Also, keep the session fun! My favourite drill for complete beginners is the Move the Cone drill which is below. It's great as it offers some competition elements which kids love, as well as good fun whilst developing their coordination. 

I hope this helps! 

Move the cone

Description:

Each player has own area with cones placed all around, and kids start bouncing the ball up and they try to hit own cone. If the cone is hit, the kid takes the cone and puts on the other player's area. The goal is to move as many cones to the other player as possible.

Coaching Points:

In this drill, players work on racquet's control under the time pressure. By giving one minute for the competition kids are forced to focus on the task and give their best. The coach can modify the drill by making teams that compete with each other or by putting everyone together and see how many cones they can hit in a particular period of time.