How to create a view to display only child nodes of a parent term?
I dont think that this way is possible,but a situation near to this is possible as:-
1. While creating a view,we have a field known as "filter criteria" field,in that add --*Content: Has taxonomy terms (with depth) (or Unknown) *


Go into the settings of this field*strong text* and choose depth of the field.**
Here Depth means-The depth will match nodes tagged with terms in the hierarchy. For example, if you have the term "fruit" and a child term "apple", with a depth of 1 (or higher) then filtering for the term "fruit" will get nodes that are tagged with "apple" as well as "fruit". If negative, the reverse is true; searching for "apple" will also pick up nodes tagged with "fruit" if depth is -1 (or lower).**
this can be of help if u don't mark any node with the fruit tag,but mark all nodes with the some children tags of fruit.