An augmented reality Engine for the Construction of Pedagogical Applications (ECPA) is presented with an ECPA menu composed of two (master and slave) sub-menus as the main interface. With simple LUA scripts that allow building the application features, ECPA can be used to easily program different educational applications in a short time. To illustrate the possibilities of ECPA engine, an application called Virtual Plant For Children (VPFC) is created. VPFC allows young people to interact with virtual plants thanks to an interactive L-system for plants growing simulation. A usability test is made to validate our interface and interaction method, in which twenty-four K4-K5 children are instructed to make virtual plants grow by giving them water, heat and light.