Well one reason he may not eat much is because he doesn't have to. If he's full from milk he wont eat.
Calcium is in a lot of different fruits and vegitables too. And other toddler foods, like mum mums, or arrowroots, or gurber finger foods. Do some research (I'll see if I can't maybe find my list again, I'm afread I don't have it on hand) Many real fruit juices do as well.
Keep trying with foods. The more you expose them the more likly they'll try it. Sometimes you have to introduce the same food 5-10 time before they even try it.
We did start early will a policy in our home, its not exceptable in our home not to eat what you get. Admittedly this stems from my parents, but I think its the way to go for our family. It works pretty well too. Since the introduction of solids, DD was expected to at least try everything, we have a one bite rule here, one bite or nothing, we don't give an alturnative. Now if she tries something (like honey, she hates honey) And we know that she's tried it, we give her something else, I will then try that food again in a few weeks time. Worked wonders for peas for us for example. One of the few foods DD didn't take to right away, she was expected to try it and you know after actually trying it 4-5 times she loves them now.
I found with DD that she doesn't like chunky foods, so stews and chillie she's not a huge fan of. (I don't really like them either) She's never been a big eater of puries, or the toddler meals (chunky baby food) so we went to finger foods. Bread with butter, crackers with cheese spread, green beans, brocolie (her fav) squash, onions (yes she like raw onions and garlic too) spegettie, ravioli, noodle soups, Grilled cheese is a fav and you can make that with little to no fat, and the list goes on.
There is really not much she wont eat. Spicy is about it, not a huge fan of spicy, or too sweet, she's not a fan of cookie, cake, or things like that (not complaining)
Its not about forcing them to eat, but encourageing them to try new foods. Make it fun, but make sure they know you mean business at the same time. When DD finishes her entire meal, especially if its a new food, she gets a small treat. Getting through the picky stage is going to be a lot easier now then it would be in a few years. Firm, consistent, but with some flexability, so they try it, but if they really don't like something give them something else, and try again in a few weeks. If you only stick to the foods you KNOW he'll eat, eventually thats all he'll eat.
DD has never been a "picky" eater, but when she was having to much milk or water or juice she wouldn't eat. She's still like that. If she drinks to much she isn't hungry. Its all about balence.