The editor at SmallGroups.com recently posted on Facebook, "Get comfortable with these three words: 'I don't know.' You don't need to know all the answers, but offer to find out."
I agree with that good advice, but I'd take it one step further to help your group really grow. (This is a great discipleship opportunity for you!) Rather than saying "I don't know but I'll find out," try saying, "I don't know but let's all research that before our next meeting. Here are some places you might find the answer..." Provide some Bible passages to look up, sound biblical websites, or a minister at your church. If you don't know these off the top of your head, find out and email the info to members as soon as you can.
This gives ownership to group members and helps them learn how to discover answers for themselves. People retain information best when they discover it for themselves. And when they come ready to share, you're developing them as future leaders.