I've always been (almost graphically) honest with my 6yo daughter, as an example she loves sausages so I felt she should at least understand that it's parts of a pig minced up. She does take an interest in which specific bits of an anatomy she's eating or helping to cook... so she's heading towards a career in medicine, or for serial killer infamy.
She may well get a conscience about eating animals in time (I find many young girls do at some point), but it's her choice and as long as she understands the issues then I've done my part. It's disgusting that parents let their kids eat so much sh1te like McDonald's without at least making sure they understand what it is. Mind you, some of those parents are possibly as ignorant on food origins as any child.