you can get multi vitamins and vit c's for little ones - I used Pentavite (I think thats what it is called, comes in a white and orange box) with Charlotte I think when she was your DDs age. It is not so easy when they are little and only just eating, but BF makes it easier, so up your intake - you can't OD on it, you will just pass what you don't use through urine.

Now I give charlotte chewable vit c tablets every day, she loves it. I tried the liquid squirt ones, but she hates them lol so now I squirt them into her porridge in the morning.
So if you can get your hands on some liquid squirts (check with your chemist what age they can have them from) and put it in her water cup, on her porridge, etc.

Of course nothing is as good as fresh and natural fruit and veg, but getting them to eat enough at that age is so hard! lol
Kiwi fruit is MASSIVELY high in Vit C, as are black currants, oranges/citrus isnt the best for little tummies

Charlotte started at day care a couple of months ago, she only goes for a couple of days a week, but I found she was getting snotty and picking up a cough etc every time she was there, which is great in terms of her immune system, but I dont want her sick all the time! So I actually bought her a kids chewable multi, as she has become quite fussy with her veg eating recently, she loves them has one a day with her vit c and I have noticed a huge improvement in her.