She was 13 kg in Dec, 13kg in April this year and 12.5kg today 
She had cancer (Wilm's tumour, removed at age 7mo) but has not had any problems since. She has had chicken pox recently (in April). She doesn't eat a lot but she does eat 3 times a day and she eats a good variety of food - she is quite fussy these days but I assumed that goes along with being 3.
She eats very little high calorie/calorie dense food but we do add butter to her meals, offer icecream which she occasionally has, and allow juice as well as water, and cups of very milky redbush tea, little biscuits and crackers as snacks, yogurt as often as poss.
I read about gluten intolerance recently but I just think that she would be having severe problems re: pooing and tummy aches and she very rarely seems to be in pain in relation to these. She has no problem pooing as she eats vast amounts of fruit. She sometimes complains of tummy ache but never to the point of tears - you can tell when a child is really in a lot of pain, and she isn't when she says she has a tummy ache.
She does look rather pale and she is very petite all over, no fat anywhere, but she has bags of energy most of the time. She doesn't sleep very well.
She gets colds quite often. We give vitamins but not very consistently.