If your desire is to stay home with your children - by all means do that. If you were to get a job simply to say you got a job associated with your degree, you would be miserable as internally you'll still want to be home.
The important thing is you have the degree - with how easy it's becoming to cross-train people these days, simply having a degree, regardless of subject area, is the important thing, as it demonstrated your persistence to finish it. This speaks volumes to a potential employer. Also, if a few years down the road you decide you now can or want to go to work more in your field, it will be easier for you to pick up refresher courses to get yourself back up to speed with current code/laws/practices vs someone who doesn't have the degree.
If you like your degree and do hope to someday get into the field, since the area of medical billing has really gone national since HIPAA, it would be easy to keep yourself current with code sets by visiting
www.cms.gov and look up current releases to the code sets published. Just like modern electronics, these code sets are changing all the time, so anyone in the field will need to keep refreshing over time, so it would just be a matter of brushing up on the latest & greatest whenever you choose to go back. People in any field need this (teachers have to take periodic training, computer programmers, etc...).
The other thing to consider is given today's economy, there are several people that are now taking jobs in areas they didn't get their degrees in, simply because it's the only places hiring. So changing careers is not an uncommon thing. Again in those cases, if you already have a degree, you tend to be more "hirable" over someone without a degree.
One last thing - my sister was in a situation like you shortly after she was married - she had just gotten her degree in psychology when she got married, and a year later they had their first kid. She worked one year in her field, but was miserable because she always wanted to be a stay at home mom, so she quit her job and was a mom. She now has 5 kids and is home schooling, and loving every second of it. She has no regrets, nor does she feel she wasted time with her degree, because she knows the time she put into getting her degree was all a part of her getting to where she is at today. She wouldn't change a thing.
So congrats on such an amazing accomplishment - and since you have the opportunity, take full advantage of being a stay at home mom if that is what you truly desire!