Many children step out of the way when a pitch is coming in because they are afraid of the ball hitting them. It is a common problem that all coaches face. It is the coaches job to teach confidence and show the children that if you hit the ball it won't hit them!!!!
Here are some suggestions to help:
1. Have the child take a wide batting stance so their feet are more grounded and it is harder to step out.
2. Possibly have the front foot closer to the plate then the back foot. That way they are slightly leaning forward and will find it harder to move backward.
3. Practice by putting a bat or board at the back of their feet. So they can tell when they are stepping out or away from the pitch.
4. Build up the speed of the pitches gradually so that they fain confidence in front of the ball.