GREAT advice. Wide body aircraft makes such a huge difference on a long haul flight.
We did BOS to HNL direct, which is the longest nonstop domestic flight in the world. Kids were 5 and 2, and my wife was 8 months pregnant. The flight out was absolutely flawless. Leaving at 8am local time and landing at 3pm Hawaiian time was perfect, and the kids were asleep in the hotel room by 5pm.
We will *not* be doing the return flight direct with kids again. We did everything right, but they just couldn't sleep, meaning we didn't sleep. We landed at 6am Boston time, and I was so tired driving home that it was legitimately dangerous. On our next trip, we're going to take an extra day coming home and do HNL late morning to LAX evening, spend a real night sleeping in a hotel, then a separate flight LAX late morning to BOS evening.
I'll add that a flight this long is where I'd consider an upgrade to Premium Economy to be worth the money, especially if you can get a bulkhead row. The Hawaiian A330 has a little cabin of just 12 seats in between first class and the rest of the plane, and it's super spacious and private.
OP, I would definitely be sure to buy a ticket for the baby. 6 passengers is a great number because you can do 3-3 or 4-2, depending on the plane, without needing to sit next to any strangers.