Just to say I very much disagree with "Anonymous" of January 17th:
1) Intuition IS important in science, and here it was used to come up with an interesting hypothesis. Yes, there has to be rigour and careful logic following up and testing ideas, but where do those ideas come from in the first place? Where would science be without intuition of those who made the great jumps?
2) "anonymous" of 17/1 lays into your post for not having controls, sufficient statistics etc.. but you don't for a minute claim that you had. Indeed you end your post by saying it would be interesting to test the theory with a control group (which implies you realise you haven't yet tested it scientifically).
3) Complete rubbish that a little lemon juice would have killed children a hundred years ago (indeed a bit of vitamin C would have been good)
I guess the project has ended, but would have been interesting to have the discussion with the kids about how you would test the theory properly. E.g. you would need to have a control group. I can't see how you could make it a blind test as lemon juice in water is pretty distinctive, as is taking a few lemons home. Some modification would be needed! Without a blind test you've got problems with placebo effect. You've also got problems that say the lazy ones who choose not to take the lemon drink at home, well maybe they were just more ill with the cold, or somehow were more susceptible to a cold, or something else we've not thought about.
If some of these kids as a result of the discussion, next time they buy something from a pharmacist or herbal remedies store or whatever for a cold, they think about why they should believe the drug is of any use to them and whether it has been scientifically tested, well, then they're way ahead of most the population.