The purpose of this study is to investigate the importance of usability in user interface (UI) design of mobile educational
applications (MEA) designed for children aged 4-5 years. Usability testing was conducted with four children to evaluate the UI
design based on the children’s mental model in addition to the quality of their learning experience. An eye tracking glasses was
utilized to capture the children’s eye movements while the usability heuristics was used to collect the descriptive data regarding
the interface design. Results indicated that the usability study can be considered as a multi-stage problem solving process where
it analyses and foresee how the children use a product and the actual first-time users’ intuition of their design experience and
learning curve. The observation, eye tracking data and usability testing of the MEA with the four children validates that the UI
application was based on the developers and designers adult mental model and guideline or own assumptions. This paper ends
with a suggestion of a UI design guideline of design elements and principles for designers and developers to adhere when
developing MEA for children.