I've just seen some great advice and thought I'd share it...
Instead of asking your kids how their day at school was try something different.
Like, "What can you teach me that you learned today?"
Or "What made you laugh at school today?"
Or "What was the crazziest thing that happened today?"
It might seem a little odd at first, especially if the kids aren't used to this type of conversation, but if you persevere you're likely to find that the conversation goes off on all kinds of tangents.
You'll find out more about your kids' days, more about their interaction with firends and teachers and you're likely to have a great laugh together.
Let me know how it goes.