First and foremost would be to identify the source of the jealousy. Once this has been identified you can help the children learn ways of interacting while positively expressing their feelings. The most important thing is that the children understand that it is NEVER "wrong" to feel a certain way, but there are "wrong" ways of dealing with and expressing those feelings! How can a child even begin to label their feelings without a guide to help them understand the feelings? I know I wasn't born with an inate ability of understanding my feelings.