My dh turned veggie when he was 7 or 8 when he realised that animals didn't die of natural causes and people then went round picking them up. He will not touch anything that involves an animal dying to make it.
All of my kids are veggie too, the older 3 was by their own choice when they saw slaughter videos and when on holiday they saw the carcasses hanging up in the supermarkets abroad.
Most people don't associate what they see in a packet in the supermarket with animals being killed, funny though that may sound. If more people thought about what happened in slaughterhouses, more people would be vegggie.
p.s. did you know that red smarties and red m&m's are made from crushed beetles? and products using gelatine are made from animals' skin, hair, nails/hooves and stomach linings, amongst other things?