This paper builds on previous research which outlined the development of a framework of scientific enquiry within a play-based curriculum for early childhood. For this paper, in order to help to mediate children's observation and exploration as part of their play, we propose that practitioners need to have well-developed skills to ask open-ended questions. This would empower the children to gather evidence to substantiate their scientific ideas and thus advance their scientific thinking. Engaging children in this type of dialogue is not an easy skill for all practitioners and our research aimed to provide support for staff and evaluate the impact on the children's learning. We found that staff improved their ability to ask open-ended questions and this enabled us to extend children's play from observation and exploration to developing scientific enquiry skills, such as explaining, justifying, predicting, testing, reflecting and evaluating.