RMT general secretary Bob Crow said the child, who strayed onto tracks on the Bakerloo Line, could have been electrocuted.
"With London Mayor Boris Johnson mouthing soundbites about driver-less trains and de-staffing the Tube at the Tory conference, yet again only the quick intervention of a driver prevented a 12-year-old boy, who had managed to shimmy up and over the inner car barriers and out of the train, from getting hit by a moving a train or electrocuted on the rails.
"Management have rightly called an investigation into this shocking incident but this does not go far enough for RMT safety reps. We want a meeting to review the whole de-trainment process and a return to a safe way of working."
More top news
Model Rosie Nelson writes for ITV News, revealing why she is calling for MPs to pass a new law protecting models from becoming too skinny.
Amid calls for new laws to regulate the size of models, we look at how the face of fashion has changed over the past 60 years.
Amid calls for new laws to prevent models getting too thin, ITV News speaks to three women in the fashion industry to get their views.