Your kids will enjoy this experiment from The Teachers' Corner. Dish ice cream into two bowls, and pour just enough milk onto the ice cream in one bowl to coat it. You'll notice that the ice cream you just coated tastes colder than the ice cream without milk. The reason is that when ice cream is made it contains bubbles. When you eat it, those bubbles slow down the heat particles moving from your warm mouth to the ice cream. Milk doesn't have those bubbles, so the heat moves faster -- and your mouth feels colder.
Have the boys in your class wear dark shirts to school on a spring day, and have the girls in your class where light or white tops to school. Go outside during a sunny time of day and have the students sit on the ground. Ask the students to raise their hands when they feel uncomfortably warm. You'll notice the dark-clad students getting too hot before the light-clad ones because dark colors absorb more heat.
This experiment works well during the last week of August or the first week of June, if you're in a warm climate. Take your students outside on a sunny day to the school parking lot. Crack an egg and put the yolk and white down on the black asphalt. Watch the egg fry on the hot pavement. This will illustrate the heat that radiates out from the sun to the earth.
The energy we feel in heat comes from the kinetic movement of the particles in the air. Bring a large plastic storage container and four or five "super balls" to class. Have students gather around the plastic container while you hold the balls in your hand. Without kinetic energy, they don't move. When you give them kinetic energy by dropping them into the container, they will feed off each other's momentum and continue to bounce in, around and even out of the container. That's how heat particles interact as well.