STEM is an educational practice to integrate science, mathematics, engineering, and technology within the formal and informal context and it provides practical opportunities for the child to make sense of the world holistically. Moreover, the most important benefit of STEM activities for children, including engineering design, is to improve or support children's science and mathematics skills and social-emotional development. In this study, therefore, it was aimed to investigate children's science motivation as well as their usage of scientific process skills during inquiry-based STEM activities including engineering designs. Fourteen 5/6-years-old children included in the study and classroom observations, pre and post interviews were conducted to collect rich data. The findings revealed that children frequently engaged in STEM activities by employing at least one of the science process skills and they used engineering thinking apart from the science process skills. Moreover, following inquiry-based STEM activities, children have recognized science as an area of activity, and there have been positive changes in their motivation towards science.