Assuming that you are talking about this field
<input name="vetname" type="text" id="vetname" value="<?php echo $row_Child['practicename']; ?>" size="35" />
then you need to filter your recordset by the value posted from the child select list on the previous page.
To do this open up your recordset in Dreamweaver in simple view and from the filter menu choose the id of the recordset then choose Form Variable from the drop down below that and type the name of your form field into the text box, in this case child. Save your changes and try it in a browser. the field vetname should now contain the practisename after the previous page is submitted.