Los Angeles, Oct 22 : Pop icon Madonna paid an emotional tribute to her children when she kicked off her electric Celebration tour - with five of her six children taking the stage alongside her. Rocco Ritchie did not embrace the superstar's return to stage with the same enthusiasm as his siblings, reports Mirror.co.uk. In the wake of her dramatic collapse and rush to hospital in June, Rocco has told his friends he worries she will push herself too hard and fall ill again. One of his friends told Mirror.co.uk: 'Madonna is a notorious perfectionist and Rocco remembers her previous tours well - she has a habit of exhausting herself by pushing too hard because she cares so much. He is really worried that her health will suffer if she does the same thing again.' Rocco's fears are justified after the 'Material Girl' hitmaker contracted a serious bacterial infection which left her fighting for life earlier this year. But the Madonna who exploded on stage at London's 02 Arena - watched by Rita Ora, Taika Wahiti and David Walliams - seemed unstoppable. Four decades after her debut, her vocals sounded unchanged as she launched into 'Live to Tell', 'Crazy for You' and 'Vogue'. And she was at her raunchy, provocative best for 'Like A Prayer', flanked by neon crosses and half naked male dancers. During the show, the icon's voice was heard claiming that the most controversial thing she ever did was to 'stay around'. /IANS