private void BtnAddNew_Click(object sender, RoutedEventArgs e)
        {
            Class classes = (Class)comboBoxClass.SelectedItem;

            if (txtboxFirstName != null || txtboxLastName != null)
            {
                try
                {
                    DbOperations.AddNewChild(txtboxFirstName.Text, txtboxLastName.Text, int.Parse(txtboxAge.Text), classes.Id);
                    ClearTextbox();
                    Updatelists();
                    UpdatedMessage();
                }
                catch (PostgresException ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }