There are a number of things parents need to bring to home to their children for each to be a participant in bringing peace to the world. Obviously, how the parents do so is different at each age level. When your family is made up of several different ages it means doing a variety of things at different times. If the issues that prevent or build a peaceful world are always within the consciousness of a parent, anytime one comes up is a good time to make a brief connection for children. They then begin to do so themselves.
That doesn't mean necessarily that the things to develop peaceful attitudes will be done by dividing the family. When a parent has time with one child of those of close age level there can be opportunity and time to develop awareness in away suited to that age. However, when all family members are together, a different dynamic takes place no matter what age the action may be most suited for.
For example: When do you have conversations about any of the important things related to making this a peaceful world? Hopefully, your family eats a meal together most days of the week, although I know many do not today. This is one good time for those issues to come up in conversation as they occur or are pertinent to family issues.
Those families that have a regular family meeting night could decide to talk about some things related to peace as part of their time together each week. In those conversations, as the children become older and can understand better the issues of hunger, violence, discrimination, war, etc., the discussion will deepen. The younger children will get what they can at their own level in these conversations. This is the way the younger children do with every subject. They also learn faster because they have all these "teachers" by way of parents and older brothers and sisters.
The general idea of talking about peace; what it really is; what brings it about; is basic to everything else we might do to teach children to be peacemakers. But that must not be the only thing we do. Sometimes the family needs to seek out ways to act for peace and so develop a peaceful people for the future.