As a parent of one (soon to be two), I can definitely understand where the OP is coming from. Becoming a parent certainly can change one's perspective. I'd just toss out something I've discovered, which I think mentioning (albeit a little off topic). I am of the opinion that you should find something you're truly happy doing so that you can feel fulfilled while you're at work; that way you can come home and be the best and happiest parent you can be. Any job (medicine or otherwise) is going to take away time from your babies, so if you're away you might as well be happy with what you're doing. This is actually what prompted me to change fields and defer residency - if I was going to be away from my kids, I sure as heck needed to be happy doing what I was doing.
Anyway, to actually answer your question, I think that as far as residency is concerned, I agree with most of the posters - PMR, derm, path, radiology, psych, maybe rad onc, possibly family medicine. All except path have an 80hr + intern year, then get considerably more relaxed after that. Derm, rad onc, and radiology (in my experience) are quite competitive. To be honest I'm not sure which ones are more conducive to part time work after residency, which is also an important consideration you brought up (there'll always be soccer practices and piano recitals in the years to come).
Hope this is helpful, and good luck!