I wouldn't want to keep my eye on a three year old, playing in a play area if my flat was on the 20th floor. As much as a parent may want to always be able to take a child outside and stay with them while they play, we know that is not always possible. A child is safer left momentarily unsupervised in a garden or back yard then supervised from a distance. Nowadays many high rise toddlers get little or no time outside for just that reason.
In other countries people do live successfully in high rise flats, but the success is based partly on the cultural norms of that Society, part of which is a more 'robust' attitude to the safety of the child. Many societies accept, as was common in Britain when I was a child, that tragedy though it be, accidents happen and children will drown, fall out of trees and get killed, run under cars etc etc. We now find this unacceptable and a family that allows a child outside below a societally approved age or lets them do anything that society does not approve of is pilloried. Look at the way Madeleine McCann's family have been attacked for visiting a restaurant within sight of their holiday flat and where they physically checked on the children at regular intervals instead of staying in and being in the next room to the children all evening.
In this country by far the majority of high rise residents are social housing residents. A microscopically small proportion of middle income families live in high rise blocks. In countries like Hong Kong families across the social spectrum all live in similar blocks of flats. This makes a difference