code: protected List<TransformationDescription> buildChildren() {
          if(children.isEmpty()) {
              return Collections.emptyList();
          }
          final List<TransformationDescription> children = new ArrayList<TransformationDescription>();
          for(final TransformationDescriptionBuilder builder : this.children) {
              children.add(builder.build());
          }
          return children;
      }
docs: Build all children.
  
  @return the child descriptions