>I want to show many values (many rows) and totals in the last row, or totals in textboxes, but showing many values of a child table.

The simplest way is to show in textboxes, by running SELECT against the table:
Select SUM(myfield1) as sum1, SUM(myfield2) as sum2 .... From ... Where... Into Cursor Mycursor
and then use cursor values to populate textboxes.