Where you hear about an athlete dying it is usually not because of exercising but due to an underlying medical condition that perhaps went undetected such as a congenital heart defeat. And believe me the number of cases is actually very small but because they receive a lot of press coverage it perhaps seems like there is a lot.
So we hear about the footballer having a heart attack on the pitch or the marathon runner dropping down dead at the end of the race. But what we don't really hear about or register is the number of deaths where obesity is a contributing factor. It is difficult to quantify but the audit office estimates that 6% of all deaths in England are caused by obesity, and that's around an excess of 30,000 deaths in a single year.
So as I see it you have to weigh up (no pun intended) your risks and benefits. There are risks in everything we do from taking an aspirin to crossing the road but we take sensible precautions and carry on. Otherwise we would spend our lives wrapped in cotton wool and never leaving the house, although perhaps not when you see the number of deaths that happen due to household accidents!
There may be some remote, infinitesimal risk if you start exercising but the benefits are huge. Your greatest risk is more likely to be a twisted ankle or pulled muscle than dropping down dead. On the other hand if you remain overweight and most likely putting on more weight as the years progress then you really are at serious risk of heart disease, high blood pressure, stroke, diabetes, cancer and premature death.
I work with patients who have had heart attacks or have serious respiratory conditions and the best treatment for them is not pills, its simple getting active. Exercise doesn't have to mean going all out pumping iron at the gym for 5 hours a day either. Recent advice is that even half an hour of activity every day can reap huge rewards, even just going for a walk. This is a great video that we use in our health services here to promote physical activity and might be worth watching as it explains all the potential benefits in a fun way.
23.5 hours - Physical Activity Health Alliance
If you are worried of course have a chat with your doctor about how you are feeling, and it would be a sensible precaution to see him anyway before you start exercising. but if you are looking for any incentive to start eating healthily and being active, look no further than those children you mention and think about the example you want to set them for the future.
Good luck!