Oh my God! That's awful! Have you tried to explain to them in adult terms why it upsets you - i.e. 'imagine how [I]you[I] would feel if I mimicked you whilst you cried...' ?

Sometimes I think people don't give children as much respect as they deserve - just because they are smaller than an adult, and altogether more adorable than an adult, that doesn't mean that their feelings and desires are less important, or their upset less acute. Being diminutive doesn't mean that you experience the range of human emotions any less intensely.