My 3 year old is gluten, dairy, and cane sugar free because of sensitivities. We are also vegetarian. She eats eggs from our chickens plus I give her both almond milk and rice milk (both without cane sugar or carageenan.) Both milks have been enriched with vitamin B12, calcium, etc. We giver her cashews with pasta instead of parmesan. We eat tortillas made out of mung beans. She is growing and healthy. LOTS of energy. I would not give almond milk to a child less than 3 because there aren't enough calories or fat. Probably the same with rice milk (it has calories, but not fat.) Coconut milk would be good. Though obviously nursing as long as possible is best. My daughter is adopted and I stopped taking medication to lactate when she was 2.5. Your child should nurse until they stop on their own.
I recently got this book http://www.amazon.com/gp/product/1592579787/ref=oh_o04_s00_i00_details I have skimmed it, but not read it fully. So far it has good info.
I also have skimmed this book:http://www.amazon.com/Becoming-Vegan-Complete-Adopting-Plant-Based/dp/1570671036/ref=sr_1_1?s=books&ie=UTF8&qid=1331525824&sr=1-1
The big thing to worry about is Vitamin B12 and fat. Both are absolutely essential for a growing child/brain. My kids both had bloodwork to check their B12 levels. The doctor's office called me and told me their levels were high and to take them off the supplements. Umm...it's the fortified milk and happy chicken eggs. So, it's easy to get enough B12 in an over 3 child. Research if you need to supplement as nursing decreases when solids are started.
Also, I took flaxseed oil while I was pregnant for omega 3s. Now I realize that oil may not have been the best choice because of its short shelf life. I now add freshly ground flaxseed to our morning smoothies and am looking at adding it to many foods I cook (although flax oil is damaged around 225 degrees, flaxseeds are not. However, you MUST grind flaxseeds or they pass right through you. And ground flaxseeds only have a shelf life of about 3 weeks, so don't buy them already ground since you don't know how old they are.) I'm also starting to experiment with chia seed. High omega 3s and they don't need to be ground, though they do absorb water and turn gelatinous. I add them to our morning smoothies. If the smoothies sit for awhile I add more non-dairy milk to get rid of the gelatinous texture.