This paper examines the differences and challenges encountered when trying to create informal blended (virtual and hands-on) engineering design STEM activities. It contrasts the creation of STEM activities for formal and informal learning environments, stressing that the differences extend far beyond the length of the activity or depth of any learning goals. The discussion begins with an examination of differences between the two learning environments that need to be taken into consideration. These differences include the physical environments, organizational structures, and the goals or reasons for the delivery of STEM activities in both environments. The paper continues by explaining why curriculum developers must be mindful of the context that will be implementing the activities, including space and time availability. The facilitators who deliver STEM activities are likely to have very different backgrounds in formal school settings compared to informal settings. Furthermore, it is important to recognize that youth in informal settings often push back when activities seem too "school-like." The paper concludes by presenting a detailed examination of the iterative process used to develop blended engineering design STEM activities in an informal setting. This process involved several revisions and tests of materials with youth in informal settings.