The two biggest reasons for children spending less time outside are the development of technology and the safety issues. The development of technology brought in our homes countless forms of having fun which is very important to children. The mobile phones, PC's, laptop's, tablets, Sony Play Station, as well as lots of technologically improved toys, made the children stay at home since they have the fun indoors, and not be interested in going outside and in nature. Also the safety issues in lots of parts in the world made the parents to restrict the children to the indoors environment.
Take a White Flower and measure it with different soil temperatures and see if it changes colors. And don't forget to record the color and take a picture with different temperatures