Smart home systems, which aim to adjust thermal comfort in buildings via various sensors, are intended to increase energy efficiency in buildings. Adults can easily adjust the thermal comfort in their homes using these systems. Smart home systems, on the other hand, are neither useful nor educational for kids. Furthermore, their education on energy efficiency and thermal comfort in buildings is vital since they will use these systems from their middle childhood years. To this aim, this study proposed to teach pre-school kids, who were between 3 and 5 years, energy efficiency in buildings via a developed smart toy. The developed toy included various sensors such as air temperature, relative humidity and air pressure sensors, a microcontroller, a carbon dioxide sensor, light-emitting diode lamps, a text-to-speech module, a battery unit, and a precision clock module. The software of the toy was written on C-based programming language and the prototype of the toy was developed by undergraduate students of Atılım University in Turkey under an undergraduate project umbrella with the help of the supervisor of Dr. Turhan. The developed toy depicted the temperature with green, red, and blue colours representing neutral, hot, and cold environments. Additionally, the smart toy spoke to the kids to warn their adults to decrease/increase set-temperature of the heating and cooling system in the room. The developed toy also controlled the existence of open windows during operation of the heating system while staying in continued-communication with the kids. Moreover, the toy warned kids to check for lights during daytime. Since the main goal of the study was teaching energy efficiency to the kids, the outcome of the study would benefit development of self-skills and cognitive well-being, enhancing energy efficiency learning for the kids and improving the awareness of building energy efficiency for adults.