Are you giving him some pentavite with added iron? That way you don't need to worry about what he's eating, as long as he's getting his vitamins and iron. Another thing that has iron is Milo. Not fantastic, but definitely a bonus if a child is iron deficient.

Would he drink smoothies? If he likes banana smoothies (or milkshakes like you said), you can add some flaxseed oil to it. You can buy flaxseed oil from health food shops in their fridge (don't get non refrigerated from Coles/woollies). This is very important for their omega 3/6 intake. You can also get probiotics from the health food shop (ask for a children's one) and add the recommended amount to the milkshake or yoghurt. These are all great for immunity and health.

Good luck. I have a 10 year old who has only eaten one kind of vegie in 8 years and that is the top of brocolli, and not much at that. She wont eat ANYTHING that we do and it's very difficult. I just try every now and then to get her to have new things, or to do the "your'e only having what we are"> Never works. Not to worry though, I have her on the above mentioned things and we have been to a kenisiologist who said she's fine. So it goes to show, they pretty much get by with what they have.

Good luck again xoxoxo