Preschool environments offer an abundance of opportunities for exploring the physical world where children can learn "engineering concepts" and "principles" (theories or laws). Yet how teachers design motivating conditions for engineering thinking has not been fully investigated. The study reported in this paper examined how teachers and young children engaged in engineering principles over 12 months. Digital video observations (123 h) captured the daily interactions of two teachers and 13 children across two classrooms during their engineering sessions. The participants were 8 preschool children aged 4.7-5.5 years and 5 school children aged 5.5-6.4 years. Different to previous studies that focus on engineering affordances during free play, the results identify new play pedagogies that support personally meaningful engineering learning of children in preschools. The new practices, named as an "Engineering PlayWorld," build imaginary situations, where children in teams act 'as if' they are engineers, meeting engineering problems and generating engineering solutions.