getChildEntities() {
    var children = this.children;
    var childEntities = [];
    for (var i = 0; i < children.length; i++) {
      var child = children[i];
      if (child instanceof AEntity) {
        childEntities.push(child);
      }
    }
    return childEntities;
  }
@returns {Array<Element>} Direct children that are entities.