There are literally hundreds of websites out there with ideas on classroom demonstrations and experiments. Many of these require no more equipment than what you can find around your house. Try to incorporate these into what you're teaching. Even better is to let the kids try the activities themselves. Allowing kids to 'get their hands dirty,' so to speak, is a surefire way to keep them interested in what you're saying.
Elementary students have much shorter attention spans than high schoolers or college students do.
If you just stand up and talk, they're not going to pay attention. Be excited about what you're saying. If they see that you're interested, than they're more likely to get interested themselves. Choose experiments and activities that appeal to kids' interests. For example, in one demonstration I've used, you place a small balloon inside a bell jar and use a vacuum pump to pull all the air out of the jar.