As a parent, it is quite scary to see your own child, whom you raised with all the love and care in the world, continuously hitting their friends with a toy car either jokingly or seriously. It is very normal to be terrified at the first glimpse of that scene. You feel that there is no way my own baby would so cruel and violent. Well, I’m sorry to burst your bubble, but it might very well happen to anyone.
In that case, you should try to recall previous events that might have triggered such behavior. Did you postpone giving attention to your child when s/he asked for it without noticing? Did you underestimate a subtle achievement s/he accomplished? Or did you show strong feelings for another child in front of yours inadvertently? The thing is, you can’t fully determine what caused the aggressive behavior but you can narrow down the options to a certain extent. Therefore, you would be able to avoid them later on to prevent the repetition of physical aggression.
You need to teach yourself how to set clear and firm limits with your child. You should always be consistent and maintain your stand. You should make sure not to mislead or get your kid confused with your rules or reactions. Make sure that you never overreact due to your frustration or panic. Remove your child from the situation and take him or her to a safe and comfortable environment. Sit him or her down and have a calm and clear talk about what happened. Make it clear that what s/he has done is wrong and unacceptable. Also point out how good and pleasant it would be to behave oppositely and act in a kind and friendly manner.
After several tries, if your child is still aggressive, try giving a Timeout (a minute for each year in their age). So if your child is three, give him three minutes out in a specific place every time. You should also coordinate with other caregivers for your child. Inform them of the issue, and agree on certain terms in case it happened when you weren’t around.
To come through with all of that, it might take quite some time, effort, and patience; but it is definitely worth it! Kids go through rough changes at times, and it is of your responsibility as a parent to do what is best for your child.