My dear,
I know what you must feel like - take heart to know that there are many kids who have had to face more responsibility than their mental age permits them too.
Some lonely mothers who know husbands are cheating on them or just too busy with work try to feel wanted by sharing their life with their kids - by putting their kids in spouses role to go with them everywhere and give theme motional support etc and they too have this empty feeling inside
Guess what I have the sure shot solution and that is spirituality.
Sit alone every day and focus on your breathing for atleast 5 mins at first.
Buy books, cds and join up meditation courses yoga sessions coz getting in touch with your soul is the only way of removing this empitiness . It has worked so well for me I want to shout it out over the tv and write it over the sky so no one suffers from depression and sadness anymore.