Solution1:
Load all the parent and child rows at first(echo out all of them). And hide the child rows of all parents, using jQuery's hide() at document ready state. Also, write the jQuery code to enable the corresponding child rows upon clicking the respective parent.

Solution2:
List out all the parent rows. And write the click event(in jQuery) for these parents to load the respective child rows via jQuery get().

See these for some of the effects: http://api.jquery.com/category/effects/basics/

I have made a quick example, you could test it here: http://jsfiddle.net/BGVzw/