Drawing Lines when Giving Ideas to Undergraduate Students
The purpose of teaching, which includes both your lectures, later guidance on their projects and also includes evaluation, is for them to learn new skills. So, the question you should ask yourself is: what skills do I want them to learn, and how do I achieve that best?

Typically, it seems to me that (if you have enough time for it), it is very important to teach them not only to read, filter and digest information, but also to search for it (Information Age and all). So, you might want to make “searching for relevant information” a required skill. But that doesn't mean you should help them acquire it. In fact, you probably should:


advertise it as an important part of what they are expected to learn
help them learn it, i.e. show them how it's done
evaluate them based on their performance


However… even if you do all that, it still doesn't mean you can't help them if they miss something. After all, if you are teaching them how to best look for information, they might realize it's a good idea to come to the expert they know in that particular field… you, their teacher. So, maybe they will come asking


  here are the relevant events I found about X in the archives… do you think I missed something?


or even:


  I see a spike in the data around the fall of 1974, and I have searched but couldn't find any event possibly related to that company, do you know of anything that might explain it?


in which cases you might want to answer them, if it seems they did their due diligence.