The little children stand squished together in a tight enclosed space Straight uniform But... squirmy Unable to be completely still
A solid phase
Then, they start to squirm some more as their boredom takes over wriggle shake some start coming off the tightly knit shape More and more lose and open spaces Until its a shapeless mass of kids Each with ample space
Then they get tired of standing around Some start playing tag Running about leaving wandering Dispersed Until finally, ... The once tightly knit figure is simply a few random kids zooming around here and there
The kids were molecules going from a solid to a liquid to a gas phase as energy was being added by the way in case you didn't get it.