Keep it simple, clear and factual, no matter what the subject matter is. Sometimes when kids are very bright, we assume that means that they can handle all kinds of complicated, wordy explanations. In my experience, the very bright kids are the ones who really want things clear and simple.
For any kind of definition question, including for concepts like love, ask, "What do you think it means?" and expand from there.
For questions about why God loves us, a simple, "Because we are his children" should be the easiest to grasp. "Sometimes we might do things that make Him angry or hurt his feelings or disappoint Him, but He'll always love us. That's what good parents do, and He is perfect."
For those questions that don't have a concise, pithy answer, say, "That's a good question. Even people who've studied the scriptures for their whole lives aren't sure. If we needed to know, He would have made sure to tell us, but what's important is that we follow the rules He's given us, so that we can be happy and learn. Some day, maybe we'll find out."
Sounds like you're a caring Mama with a great, smart child! :)