Repeatedly hitting and yelling at children can cause a significant rise in their risk of developing mental health problems. A study by Dr. Jordana Bayer at the Murdoch Children's Research Institute showed that overly aggressive parenting is putting a lot of children at risk for future problems.
Children raised in households with a lot of hitting and yelling are more frequently diagnosed with depression and anxiety, not only as children, but as adults. When children are constantly exposed to harsh treatment they learn to behave this way themselves. They often engage in biting, hitting, kicking or verbally abusing other children or even adults. They may be more socially withdrawn than other children or overly anxious, biting their nails, pulling out their eyelashes, unable to sit still, unable to concentrate or focus. They might even be diagnosed with ADHD and put on medication. However, the real problem is anxiety from the environment at home.
A better way to correct children is with choices and consequences. Allow them to experience the consequences of their actions.
Example:
A three year old refuses to get in his car seat. You have to get to an appointment and the law requires the use of the car seat. It is not optional. Instead of yelling and threatening, focus on what is most important to a three year old - to do it themselves. Then give them a choice. "You can either get in the carseat by yourself, or I can help you."
It is important to establish consequences you can live with and which do not punish the parent. If you make the consequence, "or we will not go", you punish yourself. You need to make this appointment or be charged for cancelling at the last minute. So that is not a viable option. Also make sure the consequence is something you can actually carry out.
Allowing children to make choices and experience the consequences for their choices prepares them for life. If I choose not to pay the electric bill, the electric company turns off my service. That is the consequence of my choice. Children raised with choices and consequences learn to make decisions and learn the importance of and satisfaction in doing things themselves.