You seem to want to get into the medical setting. Do that.
There are many types of positions. You could consider becoming a doctor's assistant, for which people do more doctor-like tasks than nurses do. Or if becoming a nurse, you could consider all of the options for specialization. There is quite a variety.
Try to locate a place that counsels folks for career change. My town has one that caters to women; perhaps Lima has one, too. Find out what options you have in the medical field.
Like another person had said, I recommend you go to your community college, and then transfer as necessary, rather than taking online courses, especially given what you want to do.
Going to school, perhaps full-time, raising three kids and working is a tall order. You sound like you have your heart set on this field, though. Perhaps take one or two classes to start to see if you do want to get back into the classroom. That will allow you to see the workload at school, and what changes to the duties at home will need to occur. Do not think you can do all that you have been doing at home with this new endeavor.
I think you will feel great being able to study something you enjoy. That should give you energy and enthusiasm to be able to keep up with it.
If you feel you can work and take classes, consider getting a position in the medical setting, but if you cannot find one, I wouldn't fret. I suspect that once people get used to you working in a particular capacity, they have a hard time seeing someone working in another one. On the other hand, if indeed they like you, they may make great references for that first job.
As far as going to school now, that's fine. A lot of people switch careers. You won't be alone. Go for it.