Lizzie, I am a believer of all things reincarnation and have gone to past life regression sessions myself, where I learned the most amazing amount of information. A lot of which pertained to information in my current lifetime.
Now, please, I know you are looking for help on the subject, and many people on here hold their own very differing and quite valid opinions.
Please go with your gut on how you feel about it all. I am mediumistic and I see,hear and feel things in the air - not everyone believes in it, it doesn't matter - what I experience is truly meant for me in my life, I don't have to explain to anyone.
So, with that out of the way - I think there are obviously many things in heaven and in earth that we just don't know about.
Perhaps if your child brings it up you could just do as you have done, and ask questions without leading/dismissing or trying to give them the answers. It's up to you though. When I was younger I was able to sense things that I couldn't explain or understand to adults. This caused me to believe what the adults told me - (they love me, most important people in the world, why wouldn't I believe what my parents are telling me) and the fact here is that some people tell their children that what they are seeing is not real. How do they know, are they seeing it? Children have no reason to lie, unless they fear something and are conditioned into it. It's a difficult situation as a parent to know what to do for the best - there is always a question. If my child started speaking of things like this, I would probably question them more and note the answers as I feel like children are still connected to their highest soul energy where we are conditioned not to be. Children often sense people they do not like and will stick by those they do like - it's as simple as that, they just know. We still try to be nice to people we don't like - even though we feel a sensation in our tummy/heart/head etc that we don't like them. We ignore it. Children don't.
I have heard of children speaking of times when they were in their mummy's tummies, and they are speaking of things they couldn't know otherwise.
I do have certain expectations that my child will maybe speak of things like this, I lost my Dad just after he was born and he does speak of him now, even though he didn't really get a chance to know him. :)
I am not sure if I have helped you, but you know how it goes, please just go with your own heart feelings on it all. I find it fascinating and think it is wonderful, and Ian Stevenson book will be a good read too.