Social robots can be used to motivate children to engage in learning activities in education. In such contexts, they might need to persuade children to achieve specific learning goals. We conducted an exploratory study with 42 children in a museum setting. Children were asked to play an interactive storytelling game on a touchscreen. A Furhat robot guided them through the steps of creating the character of a story in two conditions. In one condition, the robot tried to influence children's choices using high-controlling language. In the other, the robot left children free to choose and used a low-controlling language. Participants in the persuasive condition generally followed the indications of the robot. Interestingly, the use of high-controlling language did not affect children's perceived trust towards the robot. We discuss the important implications that these results may have when designing children-robot interactions.