A.J.
HI A.,
I absolutely agree with Diane S. Being consistant while disciplining is so important.
I just want to add that when you do explain that the offensive behavior is unacceptable do so in simple plain language such as "No hitting! That is not nice!" You can engage in a more in depth conversation at a later time about feelings & solutions to how he should proceed next time.
Also please understand that this behavior in toddlers is not unusual and does not mean your child is mean or a bully. They just do not have the skills to communicate their needs and using their hands is easier. And sharing is something that really isn't prefected until they are closer to 4 years old.
So when I said to discuss feelings & a solution, you need to teach him how he feels about whatever led to the incident. For example; "I know you are sad when so&so has the truck but you need to wait your turn." Also teach him to identify other's feelings as well; "You made so&so very sad when you hit him." Teach him what to do instead of hitting. "When so&so has the truck ask mommy (or teacher) for help."
Helping preschoolers to understand their feelings and the feelings of others is paramount to raising a well-mannered child. When his lanuguage skills grow, 3.5 - 4 years, you can help him learn effective communication. "It makes me sad when you ________ please stop." This process among other steps is called conflict resolution. You can google it to learn more. HTH!