finding time to volunteer

I am torn on what to do in regards to volunteering and can use some suggestions. First some background information: I just finished my first pre-med semester and did well. The commute to the college is one hour (one way) and I do the commute 5 days a week. I have two small kids, a husband and a home to care for in addition to my goal of becoming a doctor. Next semester is going to be another heavy semester - I will be taking 16 credits (all science/math) courses - and my commute will be 6 days a week - so I will barely see my family.
As much as I would love to volunteer, I also want to spend time with my children while they are still small (my son just turned 2 and my daughter just turned 7). I know in a few years when I enter Medical School - I will be almost unavailable - and will feel aweful if I don’t get in time with them now. However I know how important it is for medical schools to see some sort of volunteer work. I volunteered for about 6 months last year but I would guess they would want to see more of a committment.
In summary I want to do both (but think if I do I would probably be over extending myself and end up calling out -frequently- from my volunteer responsibilities and would prefer not to do that) and need to give the volunteer dept an answer in terms of whether I will be returning or not and frankly I don’t know what to do.

What’s your past record on volunteering? Unlike your prereqs, volunteer work doesn’t need to be in the recent past - what it needs to do is demonstrate your commitment to helping others in the community. Now, if you haven’t had much exposure to the medical world, and are trying to volunteer to ALSO meet that expectation, that’s a different story - you do need to be able to demonstrate that you know what you’re getting into. Whether you’ve already done enough to state that convincingly is really so individual that probably none of us can say what’s enough.