session.saveOrUpdate(parent);

This parent row is an already existed one and it also has some children.Now the above query is updating the parent row correctly.

Next,

int size = parent.getChildren().size();

when i print the size,it always says zero.

I also tried by setting fetch="join" in the mapping file for the Parent table.
still it says the size as zero.

could anyone tell me why the child objects are not loaded here?

Can you post your code on how you have attached the children objects to your parent object? Also, please post your mapping of your parent and child object. This will help me give you a better direction to resolve your issue.

I actually have a blog about updating the parent-child object relationship. You can check it out here http://codecrawler.blogspot.com/2009/10 ... t-iin.html