Gess, nobody does say they wouldn't let their three year old walk down steps unaided. But some of us would be very, very unhappy to discover their three year old alone, unsupervised, out of sight of any adult, jumping down four deep brick steps onto concrete while they were at nursery.
The steps were impossible to watch while the playground was supervised by one person - they knew that - and they should have been fenced off, just like they are at ds's perfectly ordinary, scruffy, London primary.