We had a mini grease fire in our oven once due to some spillage that hadn't been cleaned up and was caked at the bottom. It's great that you're thinking ahead, while also thinking carefully about the best way to clean (i.e., an effective method that is also least harmful to the environment and the health of your family).
What we subsequently used to clean was a combination of items, including:
>A LOT of elbow grease (a.k.a. repetitive arm strength)
>A non-abrasive scrubber (we picked up an orange plastic one at the regular grocery store, but I bet the natural food/home supply store has an even better one)
>Baking soda and vinegar (these work great for a wide variety of cleaning projects)
You might also turn on the oven for about 15 minutes at a low temperature before you start (to loosen up the items to be cleaned off the oven surface). On a side note, this is a great tactic for cleaning the microwave too: put a bowl of water in that oven for a minute before you clean and it will make the elbow work a lot easier.
Good luck -- I hope these tactics we used also work for you and your family.