I'll be a father in a couple of weeks but I've been working on a "life/work balance" for quite a while now. If it ever comes up with a client I remind them that we're running a marathon, not a sprint, and that putting in a solid 8 (or 9), consistently, week in and week out can get a tremendous amount of work done. It's really easy to work too much and burn out, even if you have a lot of experience -- and 40 hours per week is a huge amount of time if you're making every hour count.
Kudos for making extra time for your kids. I plan on doing the same.
On down side though, time is one thing, what you make of it is another. It's hard to make an instant switch from thinking about that annoying bug or tough to crack algorithm, to playing with a toddler. I often find myself staring into thin air while they are talking to me, caught in a hard problem bothering me.
Kudos for making extra time for your kids. I plan on doing the same.