My boys (4, 8 and 10 yrs) have been vegetarian from birth, they are the ONLY vegetarians in the school (gosh, as far as I know, we might be the only four veggies in the village!), and they are now (since we've discovered the truth about dairy/egg production) cutting down their dairy/egg intake, with the goal of becoming vegan like me. The older boys understand why, and have actively chosen to do this, the 4y/o (a picky eater, with a stubborn, rebellious streak!) is going to take a bit longer to adjust his tastes - but I would much rather he took a little longer to make a long-term (hopefully lifelong), happy, healthy transition, than trying to push him too hard and have him rebel.
I went into school with them this morning, as they go to breakfast club, and I spoke to the dinner lady. She was always very accomodating of their vegetarianism when they were having school lunches (they take packed lunch now for financial reasons), and she seemed just as helpful and supportive of them phasing out milk and butter at breakfast club! My 8y/o will take his cereal with straight soya milk (at least the alpro original), but the 10 y/o and 4y/o have been taking it 50/50 with dairy milk at home to adjust to the taste gradually - she seemed to understand, and be happy to do that! They're all happy enough with the vegan margarine, so that's easy... My only concerns now are milk in the classroom for the 4y/o (the school is going to order soya milk, but he may not like it!), and whether the brand that they order in is as palatable as the alpro anyway (there's so much variation isn't there?). I left a bottle of alpro, and a tub of vegan marg with her for them to use this week, and she said she'll let me know tomorrow what brand she's able to order so I can try them with it at home too!
My 10y/o has had some unpleasant comments (bullying?) from his classmates about being a vegetarian (not that it's detered him from his convictions), so I intend to keep a close eye, I think it was just used as ammunition by kids who would have been mean even if he was omni, but I know it upset him... As far as I'm aware the younger ones have not had any negative reactions about being vegetarian, so hopefully this won't be too different.
When I was in primary school, I was the only vegetarian in a small sheep/cow farming community, my 'vegetarian' option often involved the dinner lady picking the lumps of meat out of my bowl of stew at the table in front of me - needless to say I always felt sick on those days, and was unable to eat my dinner! I know there's still a long way to go, but things have moved on!