DD has had a really bad run of sickness last couple of months and dropped weight - so I started boosting her milk with toddler formula because she lost her appetite for food as well and needed the vitamins as well as the calories!! It has worked!! and she hasn't got constipated - it makes the milk a bit sweeter and also has the same milk taste - so you might want to try one or two scoops to a bottle and see how it goes? Or you could make up formula normal and then try watering her milk down with it little by little till she's used to it (ie 1/4 formula to 3/4 milk. Toddler drink is over-marketed but personally I'd prefer to use it for a while than a sugary nutritional drink like milo - and watch the nutritional supplements in the other sections if you are looking out for soy as they are mostly based on soy protein isolate. Hope your little one feels better soon - it's so miserable when they are sick.