Reactive Publish, nested query

I want to publish a document and its child in the same collection reactively.

I tried to use nested query and I am returning single cursor :
Posts.find({_id: {$in : Posts.getByID(id).childs.concat([id])}})
but it is still not reactive and I can’t get the new childs,
is there any way I can make this to work? I am not big fan of publish composite for performance.