By nature children have a tendency to trust. A healthy child will have three kinds of trust - in Divinity, in the goodness of people and trust in oneself. If you keep telling children that everyone is a cheat, the child loses trust in the people around and society in general. Their personality, talents and communication skills shrink. Their interaction with people suffers a great deal. As parents we have to build these things in a child. Do you encourage them if they come to you with complaints? Or do you mould it to something positive? You have to play a balanced role. If they get swayed away by somebody whose habits are not so good, then you have to point out their mistakes and bring them to the centre. But if they are telling you negative things about somebody, then you have to point out the positive. 
We create an atmosphere around us. If we create an atmosphere of negativity, distrust, or dejection, they are going to reflect and bounce the same thing on us. But, if we create an atmosphere of trust and children grow in that atmosphere, they become brilliant.