Introduce heat (also called thermal energy), and that it can move from place to place. Then do activities that show different ways that heat can move:

Conduction activity: heat conduction in different materials.

Convection activity: heat convection demonstration.

Review that both conduction and convection need molecules to transfer the heat energy.

Radiation: Ask students to sit in a circle, and move around the circle with an incandescent light bulb. Allow them in turn to feel the heat coming from the bulb from a distance (don't let them touch it or they will get hurt). The heat coming from the bulb is mostly by radiation - an energy that can pass through empty space, it does not need molecules to be transferred. (Only 1/8 of the heat energy is by conduction and convection.)
The sun is a source of radiation.
Radiation is also called infra red.

End with the heat sources activity.