How to discipline children in the classroom?

You have to be consistent. If you ask them to do something they need to know that there will be consequences right away for not listening. It sounds like you need to review your rules. Remember to keep the rules simple and don't have more than 5. Whenever one (or both) of them breaks a rule, make sure the consequence is immediate. For example: if a student is tipping their chair, take the chair away. If they are talking to each other, separate them (you may have to stand between them). Remember, they are still really young. Try to make the program fun or competitive to keep them on track. You can't expect them to sit still for too long, if they are getting antsy, find a way to add movement to your class. And they will probably work pretty hard for stickers or dollar store toys (get parents permission to give toys).