Ask yourselves whether you would be comfortable answering such questions. I also urge you to take it further than just ask questions - be curious, care about these issues and see how you can help. Educate yourselves and help educate others. Because we need allies in this fight and you might just be that ally if you care enough.
There are many difficult things in life and we can't always shield our children from those things. I think it's important to help children to ask questions about things that are difficult to understand, we may not always have the answers, but maybe that in itself helps children see that some things in life are hard to explain, even for grown ups.