Telling eight year olds not to do what they have been coached to do is stupid. It defeats the purpose of sport which is to practice hard and perform at ones best. I don’t participate in a sport that caters to the idea that there are no losers....when one loses he should work harder and always attempt to improve. Protecting kids from disappointment does not prepare them for life, it sets them up to fail.
The Battle of Waterloo was won on the playing fields of Eton.
If they are going to have a mercy rule, in football, they have to end the game, unless they have a big enough bench to substitute second string players. My guess is that is the intention of the mercy rule, play everyone. I know that parents get mad, but that is the way grade school sports are run these days.