Outdoor play is critical for the wellbeing of children. In cities, access to unsupervised outdoor play is limited by a host of obstacles. Many of these limiting factors can be mitigated by environmental design. The following identifies seven design principles for urban public landscapes that support play for "tweens" (children 10 to 13 years old). We developed these principles using a mixed methodology that included a literature review, an analysis of qualitive interview transcripts with tweens, and a precedent study of playable urban landscapes. The Seven Cs for Tweens principles include: connectivity, community, cues, character, child agency, challenge, and comfort.