I have 3 kids (8, 6, and 3) and a bun in the oven who have always been vegan (I've been vegan for 15-ish years). There was some controversy when my first was two and they tested him for everything (nutrient deficiencies, kidney and liver function, x-rays, etc.) and send us to a dietician and everything was fine. Nowadays when my kids have a check-up, we get such positive comments about their varied diet ("so nice to see kids that don't just have chicken nuggets every day for lunch").
I think there is a lot of pressure to 'get it right' when you're raising vegan kids, but I also don't think it's very tricky and that a healthy varied diet is all you need. (I took a course in nutrition earlier this year and some courses on childcare, etc. and the bits on veganism were really laid back and the courses were more focused on basic childhood nutritional needs (they need a bit more fat than adults and they need good sources of protein, calcium, and iron, and vitamins A, D, and C).)
Also, kind of OT, heart disease starts in childhood http://nutritionfacts.org/video/heart-disease-starts-in-childhood/
(and maybe even in the womb http://nutritionfacts.org/video/heart-disease-may-start-in-the-womb/
) -- I was diagnosed with high cholesterol (like heart attack levels) at age 10 (we ate healthy food and whole grains and veggies and such, but we also ate meat, dairy, and eggs). This is one of the reasons I went vegan in the first place (I tried loads of different cholesterol-lowering diets and none of them worked) and one of the reasons I give people for raising vegan kids.
is one of my favourite websites for plant-based (vegan) dietary recommendations because he backs everything he says up with scientific studies and there is some kid-related stuff there, too.
Good luck, and be sure to take your ovaltine
B12 supplement. :D