I agree with your observation about scale. It’s interesting to think about where the idea of parents having obligations to their children—or of individuals having a special obligation to their community members/fellow citizens—comes from. I think these might come partially from a notion of neglectedness. My child is not more important, morally, than any other, but I can assume most other children already have parents looking out for them, so my child is counterfactually the most neglected cause (and the most tractable cause among children I could care for).
(and sadly, it’s not true that we can assume most other children already have parents looking out for them. Or at least, for your argument to work you need to replace most other children with all other children)
Neglectedness is usually taken to be the amount of resources going into a problem. You can measure the resources by “parenting time” (what about orphans, by the way?) but in many cases it is not the most important resource.