You can't insert just one item into a listbox. You have to send in the whole string. So you need to make up a cell array of strings and then send that in. for what you did, no for loop is needed:
listboxItems = scchildren1(1:z);
set(handles.listbox2,'String', listboxItems );
If you then want to highlight/select a particular item in the listbox, then is when you set the value property:
set(handles.listbox2, 'Value', someIndexYouWant);
Note that if you have multiselect on then someIndexYouWant can be a vector. if it's a single selection listbox, someIndexYouWant must be a single number.
