Granny, Ensure might have a bit too much milk in it, and could cause diarrhea, but someone may correct me on this. It is mostly sugar, proteins and vitamins. But I suppose it will do if you don't have any other poultry vitamins. Weak chicks do well on vitamins and sugar in the water. I would get this little one in his own brooder and under more heat. 98 to 100 degrees. Weak babies need more heat than healthy ones. Make sure he at least drinks. Offer him up hard boiled eggs as well. Great emergency food for babies. Weak or sick babies don't eat their regular food much, so egg is a great food to get them going.
If the chick fell in the water, you might want to dry him off so he doesn't chill.
You just HAD to go and do it!