S.T.
My husband wasn't in med school but he was in the NYPD academy and became a rookie cop (also as a career change at an older age) less than a year before 9/11. He's worked in a few special units that required extensive long hours - sometimes round the clock. He studied to become a sergeant and a leiutinent. There were many years when he came home to sleep and not much else. In the year following 9/11 he often worked 18 hour days - 6 days on with one day off in between, that was after a month of working 18 hour days with no days off.
When he had time off he wanted to sleep - and my kids were preschoolers at the time and not quiet! I frequently took the kids to family's homes. We saw a lot of grandparents on both sides, aunts and uncles, church groups, etc. We tried to schedule when he'd be home and awake so we could catch up with eachother. then we'd leave him to his own devices again. For my husband, and perhaps for yours, they need peace, quiet and absense of distraction. So finding place to go with your kids may be one of the best ways to support him.
anohter way to support him is to have meals ready for him to eat with very little advance time and preparation - and at odd hours and will often not match your mealtime. Leftovers go in a plastic container (plastic bags work well for many things), use a sharpee to label the name of the meal and date. Just cross it off for the next meal. That wy when he's ready to eat at 11:00 not at 6:30 he can easily pop dinner in the microwave.
Now 14 years later it's not dramatically different except the sense of panic & urgency is gone. You will all survive this. Your kid can help him study (flash card type stuff)
Good luck mama - it will be good once done. i know it will!