I'm no policy maker, but here's what I think needs to be understood and then facilitated (made to happen):
First, the one issue I'd have with such an app is that it would make it far too easy for sexual predators to lure kids into their grasp. If a child can leave their house and be given walking directions to a "friendly house" that an app on their phone says is safe, just imagine how easily horrible people could take advantage of them. It's likely that those kids would never be seen again, or at least not for years or decades after being kidnapped like that...it's happened before and that would be my only fear.
We have to accept that preventing broken families is impossible. Sad as it is, it's just reality. That said, you can absolutely work to make the situation better for as many as possible. What we need to first ensure is that we are not in any way making it easy for the government to destroy a family that is in fact good and the only issue is the child thinking life is worse than it is. Bad as it is that some bad families exist, it'd be worse if a kid was able to break one by throwing a petty tantrum and calling a hotline that created a legal basis of action for someone to take the kid away. That would gut the parents to no end.
That recognized, I'd say we really just need to work on improving CPS (child protection services) and foster care. If someone thinks something is wrong with a family, including any member of that family, they can call CPS and a court hearing will be scheduled wherein the situation of that family is assessed. If the parents are truly abusing a child for ANY reason (I'm talking things like not giving them food, shelter, medicine, or truly serious verbal abuse, not just verbal disagreements with something the child claims to say or be) then the courts will assign the child to foster care. The issue with foster care is the adoption system is hugely expensive and time consuming. Part of that is to ensure that only good people get through the process to take newly-adopted kids home, but part of it is also inefficiency that could be streamlined.
Sorry for writing so much. This issue is just a sad affair entirely, because the only way to ensure kids get help is to make the process so clunky that bad people don't try to abuse it.