After losing his daughter to a horrific incident a troubled rock star forms an unlikely bond with a neglected child , changing both of their lives forever.

Good points above>

How old was the daughter he lost? Agree, doesn't matter how she died only that it was unexpected. And age of boy is important here too to give real picture..

Rockstar troubled by gambling? alcohol? failure? Similar childhood with the boy? Maybe the the boy was a friend of his daughter's who is lost without her??

Maybe this boy is an illegitimate child he didn't know about that gets dumped on him?

Maybe this child is the son of a groupie who keeps following him around.

Maybe this child helps him write real music again, Maybe they write together.

This has a lot of scope - relationships are what makes us want to watch and children can always make it more heartfelt.

Your logline kind of answers its own question.
Man loses his daughter, Man form bonds with a neglected kid, problem solved.

Because your logline answers its own question, there is no conflict, and story is conflict.

What is the dramatic conflict that needs to be resolved in your story?

Look to highlight conflict in the relationship, in case the other adjustments don't do it. His grief may make him unwilling to help anyone at this time, it may be the particular trouble,? something on the kid's side, etc.