Good tips!

Do you really have that much choice of schedules between London and the West Coast? I flew that route a lot, both as a passenger and worked it as a Flight Attendant. With a few hours' give, most follow a set pattern. Over to Europe is usually overnight (always?)

On some aircraft, like the 747 which often do this route, you can find two seat rows towards the back of the plane. Would be nice to be on your own with a window.

4 is a very reasonable age for travel. They understand and can ask questions. So much easier than squirmy toddlers. It's still a long trip but I'm sure he'll find it an adventure. Just pack lots of activities and bring the rechargers for anything electronic (in case of delays).

Here are my non-commercial flying tips. I just updated it and added a photo.
http://flyingwithchildren.blogspot.com