I'm a newish dad and full stack dev. I've found that what's been most effective for me, aside from spending (admittedly, far too much) time coding in the evenings before sleep, is making a concerted effort to share whole-day responsibility of the kids on weekends. I'll take the kids on one day, my wife will take the kids on another day. We trade off during the week too so we can both have large stretches of uninterrupted time.
Exercise (and for me, meditation) are important balancers too - don't neglect them for the sake of coding, you'll find that you just get burnt out.
Although I don't usually get full-days this has become really helpful for me. 4 or 6 hours of time to do something is incredibly productive for me now.
Exercise (and for me, meditation) are important balancers too - don't neglect them for the sake of coding, you'll find that you just get burnt out.