The Young Peacemakers Project Book, by Kathleen Fry-Miller and Judith Myers-Walls is a sweet collection of simple crafts and activities to engage children ages 3 - 10.
The authors frame peacemaking in terms of learning empathy and responsibility for others. Section I focuses on caring for the environment, Section II emphasizes understanding people (in all our difference) and the ways that differences are sometimes used as the basis for prejudice and discrimination. Section III provides kids with some concrete activities for problem solving, although this is definitely not a comprehensive conflict resolution program. Rather, the activities are geared toward 1-time activities that could open up more conversation or deeper work.
The book is old (1988) and does not address internet resources at all. However, it is a lovely collection of ideas that seem very age appropriate for younger children.
The book is out-of-print but there are used copies available.
There is a second edition that is still in print.