Sorry, just reviving this thread as I wanted to add things that we are doing with my 14 month old daughter.
- For vitamin C - we are giving her some acai berry powder + camu camu powder mixed with drinks or food
- Spirulina - we have included this as a part of her diet by adding it into a smoothie
- Fish oil - aside from eating oily fish at least twice a week, she has some fish oil
- gelatin (great lakes unflavoured kosher gelatin) - before bedtime she has a teaspoon of gelatin mixed in water. Whilst I dont know if this builds immunity or not, gelatin is good for health (
http://wellnessmama.com/7419/12-uses-for-gelatin/) and it helps with digestion.
We cook food for her in avocado oil or coconut oil as it is high in 'good' fats.
My daughter is allergic to dairy, and we avoid wheat/gluten based products as much as possible. There's a small bit of gluten/wheat left in our diet (oats + wheat flour for making indian flat breads i.e. chapatis) but the wheat flour is a very small portion in order to assist with getting the right dough consistency for rolling them out.
We eat a lot of amaranth (including amaranth flour for flat breads), quinoa, buckwheat, wild rice, millet etc. aside from as much organic vegetables/fruits as possible. I prefer using homeopathic medication as much as possible instead of conventional medication.
We had a tough time with my daughter in the initial 6 months since birth as we were dealing with reflux due to allergies towards milk which wasn't detected until she was 3 months and it took a while for her gut to repair. But she's hardly ever been 'ill' i.e. with flu/fever etc. and since turning 6 months and her gut being fully back to normal, we have never had to deal with reflux either. She's exposed to all sorts of oudoor elements - we don't stop her from exploring things, putting things in her mouth within reason etc. There was only 1 time at 9 months when there was an epidemic of vomitting bug in the UK which she picked up but even that went away within a week on it's own and she was active the whole time and happy most importantly.
We have included flax/hemp seed, dates, walnuts, almonds, cashew nuts, sesame into her diet and that has also helped. M is a very active and happy girl and I feel all of the above has helped in staying healthy.