As a young 20-something, I don't need to automatically relinquish my seat to you because you are standing with a child and "pushing 40." We are all tired - because I'm younger doesn't make me less tired than you. That said, I generally will give up my seat in this instance, or to elderly or someone in a cast/crutches/etc, but you really shouldn't have "beef" with someone who doesn't.
I didn't want to pull this line out, but a lot of people have hidden ailments or otherwise that they need that seat for. But you can't see that and wouldn't know unless told, so instead you have beef with them for "making" you stand.
You are always welcome to wait for the next bus, take a cab or rent a car if you really need that seat. We are paying the same, and while it might be seen as courteous, just because you have a sleeping child doesn't mean you get the right to my seat, and can give me the side eye for an entire ride if I don't jump up for you.
If I got up for every child I saw, I would never be able to sit myself. That isn't really fair, is it?
Sitting on a curb is ghetto? That's pretty funny. Some of us think it's fun to sit down and watch the world pass by without needing a seat. It has never struck me as "ghetto."