I think your sister needs to spend more time in the real world! It's what kids do, and it's a lot better than most of the nutritional horrors they're subjected to these days!
I agree with the general setiments - whilst ketchup does have a lot of sugar content-wise - for starters children are unlikely to be drinking it and at meal times your chewqing stimulates enzymes designed to cope with sugars and acids etc.
Get them on to HP Brown - for real men ;)