public List<Group> getAllChildrenGroup(int parentId) {
        List<Group> list = new LinkedList<>();
        Connection connection = ConnectionManager.getConnection();
        if (connection == null) {
            logger.log(Level.SEVERE, "Couln't establish a connection to database");
            return list;
        }
        
        try {
            PreparedStatement ps = connection.prepareStatement(SELECT_BY_PARENT_ID_QUERY); 
            ps.setInt(1, parentId);
            ResultSet rs = ps.executeQuery();
            while (rs.next()) {
                Group group = new Group(rs.getInt(ID_COLUMN_NAME), rs.getString(NAME_COLUMN_NAME), rs.getInt(PARENT_ID_COLUMN_NAME));
                list.add(group);
            }
        } catch (SQLException ex) {                       
            logger.log(Level.SEVERE, null, ex);
            return list;
        }
        return list;
    }