Haroutioun D.
As your case is a general problem faced with many teachers, my advise as Behaviour and Learning Coordinator will be to talk with the children privately and try to understand how to gain them as an ally to you.

Lubaina A.
A few years ago, I attended a wkshop called 'Positive Discipline.' I found it quite helpful especially with younger students as they tend to be 'extrinsically motivated'. This means that they need external stimuli (rewards) to assist a particular behaviour. We, as teachers, are so wired to focus attention to the negative behaviour that these students start to misbehave because they know that this is what will get your attention. So, create a star chart, for example, for the class. Everytime you see a student following your instructions, make a big deal of it and give them a star. If you find these 2 naughty ones are continuing misbehaving, tell them they have given away their star and place a star next to every other student's name on the chart. You may give a 'big prize' to the student with the most amount of stars at the end of the week (ie stand at the front of the line, sit on the teachers chair during a lesson, have lunch with the teacher, get a healthy but delicious snack from the teacher etc) Generally, this will help the disruptive ones get in order as they will see that you ignore their behaviour and focus on the well-behaved ones.

Robert B.
Generally speaking, I agree with Lubaina's advice. This is especially true when you start to consider the student's motivation for a particular behavior pattern. Some children crave attention, but are not yet capable of distinguishing positive from negative attention. It is human nature to seek out the simplest path to obtaining a desired result, even though few of us could articulate the underlying desire or strategy to achieve this end goal. As an outside observer, you can easily see that these kids want attention. As a teacher you need to channel that desire into a positive discipline approach. As Lubaina said, one way to do this is through extrinsic motivation. Notice that the suggested rewards scheme does not penalize the poor behavior. That is the naughty students never have anything physically taken away from them. Instead they lose an opportunity to get some reward. I'll extend this idea a little bit below. Keep in mind that people do things for reasons they might not understand. Because you can understand their basic motivation, to seek attention, you can plan around that, and try to guide them into a positive role. A classroom will always have space for some 'helper' to do some 'task'. For example, the first time you try an activity with a class, you may want a helper to demonstrate that activity. At the end of the day, you may want some helpers to tidy up the room. It is important to thank your helpers and when possible give specific positive feedback. In this way, you have provided an external motivation through a rewards scheme, and a space for these kids to get regular doses of positive reinforcement. One word of caution about this approach is that you need to have the patience of a saint and refrain from giving undue attention to negative behavior. When the kids are running amok, you need to have a plan to direct that energy into a positive direction.

Raymond B.
Young children require set routines for each class task and activity, Inform them what is expected in class: How to behave, when to talk, when to move, listen to the teacher and follow the teachers instructions, give plenty praise and encouragement. When giving instructions be clear and never back down or they will do what they wish. As mentioned give rewards that is clear for all to see (A star or rewards chart). Each child should be able to receive rewards.

Darryl B.
Very late reply, however Raymond mention routines. There is research and information in books and online about "predictable routines and signals". They make a positive impact on "affective filter" (anxiety).