There is only one way for a planet to change its temperature:  Either more energy comes in, or less energy goes out.  

1. Simulation Activity:  You can explore the role of atmospheric gas concentration, absorbtion of infrared photons, and atmospheric temperature using this simulation from Phet:  http://phet.colorado.edu/en/simulation/greenhouse

Through your explorations you can discover: 

How do greenhouse gases affect the climate? 

What happens when you add clouds?  

Do all atmospheric gases contribute to the greenhouse effect?

How was the gas composition of the atmosphere different during the last ice age compared to today?

2.  Inquiry Lab: 

Here is an activity created by the Institute on Climate and Planets, NASA Goddard Institute for Space Studies (2004). The original resource is a multi lesson module designed for grades 9-12.  We will be adapting Activity A, "Modeling Hot and Cold Planets" into an inquiry exploration for elementary students. 

The lesson that we will be adapting can be found here:  Activity A, Hot and Cold Planets http://www.trunity.net/files/200201_200300/200214/activity-a.pdf

The original Module, Waht Determines a Planet's Climate, can be accessed here:   http://icp.giss.nasa.gov/education/modules/eccm/