code: public int getChildrenSize() {
          final Lock lock = sharedObject.getLock(ACCESS_OBJECT).readLock();
          try {
              lock.lock();
  
              return children.size();
          } finally {
              lock.unlock();
          }
      }
docs: Gets the number of children in this tag. An efficient way to find the
  size of children.
  
  @return the size of children.
  @since 3.0.1
  @author WFF