Tips for work-life balance when doing postdoc with two very young children and a one hour commute
I'm a postdoc and I work maybe 40-45 hours a week. 

Things that make this work: 


I don't check my work email at home. I did that in the past, now I don't. I never missed something (although once in a while a colleague will call with something really urgent). 
I don't do everything around the lab. I clean up my own stuff in the lab, and I will do my "chores" but I'm not going to be involved with buying stuff, reorganizing stuff, salespeople, "better" kits / reagents, saving money, discussing the who-does-what etc. 
I don't do all the experiments I can do. I can think of many things that are very interesting, but some are just more interesting than others and you can only do so many. Maybe at a certain point what you can think of still fits in the time you have (and you're going to work more to do it), but in the end there are only 24 hours in a day, so you have to start cutting at a certain point. Why not now?
Related: I don't write long papers. I gather the proof, make a point, find the holes, plug them and that's it. I don't do certain experiments "because everybody does them" or "because 4 methods to prove we made a known compound is better than 2". And your "interesting side-phenomenon" will probably be moved to the supplementary info. 
And the most important one: I don't expect working more is getting me ahead. Good papers are. Smart questions are. A keen eye is. Collaborating with great researchers is. Of course you need to spend the time and effort and be productive, but there's no A for effort, nobody is going to think you're a better researcher because you did 20 experiments this week and even publishing a few more papers isn't going to make a difference.