The best way to help children to behave well is to give them rewards whenever they do something good which can be in the form of words, gestures and gifts. Right timing is essential as children should be able to associate rewards with good behaviour. If you give the reward too late, they may not understand what it is for.
A simple pat in the back or "well done" is usually enough to tell children that they have done the right thing. It is fine to occasionally give them gifts. However, you have to constantly check their motivation for behaving well. Make sure that it is not just because of the gifts.