The elderly who need a wheelchair I think can be lumped in with the "disabilities" crowd already, not really a separate category.

Caregivers carrying children too small to walk seems like a better solution than ensuring all bridges have ramps, but that's just my opinion.

You're obviously not a caregiver who has to carry both the child(ren) and the stroller in the stairs.

I've done that a lot actually? Regardless, I don't think our society should be specifically structured around certain use-cases, and I think it is wildly impractical to try to cater to all of them in all scenarios.