How do you prevent your child from picking up bad behaviors from his/her playmates?

Constant reminder from us, parents. We have to find time with our children always even if they already go to school or are exposed to peers. Let them feel that you trust them that they know what is good from bad. I believe if you have established a sense of trust between you and your child, you'd be confident that he will treasure the values he's learned from you at home.