Ways of engaging 12 year olds?

For part of my A level physics course, i have to teach a class of younger students about the properties and structures of solids, liquids and gases. There are several other groups doing this and are taking the approach of a powerpoint and physical demonstration and I am looking to try to break the mould and use a different way to engage the students. However i am running very low on ideas and need some help to get some inspiration. Any help from trachers or students into how would be best to engage the students would be much appreciated.