Let your child hit several balls in a row. Find a large enough hitting area to hit safely. You'll need several golf balls, a dozen or two should do. You'll find hitting matts at most golf equipment stores. It doesn't matter how good or bad the contact.
Every swing is a good shot, no matter how they hit the ball.
Don't worry about stance or grip. Give your child your total attention, praising their efforts. Attention spans will vary. Follow the child's lead. They may want to hit a couple of balls, then go pick them up.