Children live in a highly sophisticated world composed of interlocking complex systems. An appreciation and understanding of such systems is critical for making effective decisions about everyone's lives as individuals and as community members. This article addresses one approach to introducing children of all achievement levels to introductory complex systems, namely, through mathematical modeling. It highlights five main attributes of effective modeling activities. These include the exploration of a meaningful complex system, the elicitation of models comprising important mathematical ideas, the explicit documentation of children's thinking, the provision of criteria for self-assessment, and the construction of shareable and reusable models. With their multifaceted and multidisciplinary nature, these activities also serve as valuable learning experiences that link several disciplines in the school curriculum. (Contains 7 tables and 3 figures.)