"I think I can, I think I can' puffed "The Little Engine That Could." The American folktale taught the value of optimism and hard work reflecting a growth mindset belief about abilities. A growth mindset positively impacts academic achievement, motivation, and children's agency for learning. Few studies have explored how early childhood teachers can develop children's growth mindsets. We report on a study that developed design principles to assist early childhood teachers to foster a growth mindset in children in early childhood classrooms at one school in Western Australia using design-based research. Two iterations of the principles were designed and examined with teachers of children aged 3.5 years to 6.5 years of age. During three focus groups conducted at the beginning, middle and end of two iterations, the researcher and teachers collaboratively developed, reflected, and refined the principles. Weekly video diaries recorded the participant's reflections on the principles. The nine principles were found to improve early childhood teacher knowledge and practice to foster a growth mindset in children. The results from this study contribute theoretical and practical knowledge to support the inclusion of mindset theory in early childhood contexts to foster children's growth mindset for positive learning outcomes.