Who knocks over the sand castles in Lord of the Flies?

In Chapter 4, a few of the littleuns are making sand castles.  They have made a bunch of them on the sand bar and the mouth of the little river.

While they are doing that, Roger and Maurice come along and destroy the sand castles by kicking them over.  They also scatter the rocks and flowers that the littleuns have been using.

This shows that Roger, especially, is getting less civilized.  However, we will find out a bit later in the chapter that he has not completely broken from civilization because he is unwilling to actually hit Henry with the rocks he throws.