Should I pay for an extra seat for an infant?

If you can afford it, yes. Having a 'lap infant' on a 12+ hour flight is physically exhausting. Buying a seat allows you to bring your own FAA-approved car seat, which is safer and keeps the child in a familiar environment.

How do I deal with jet lag?

Start shifting sleep schedules by one hour each day for three days before departure. Once in Tokyo, stay outside in the daylight as much as possible on your first day.

Booking flights to Tokyo with kids

Prioritize direct flights or those with a single long layover to minimize stress, and always book your tickets directly through the airline's website to simplify seat selection. Plan to fly overnight to align with your children's sleep schedules, and aim for arrivals at Haneda (HND) rather than Narita (NRT) to cut your commute into the city by at least 60 minutes.

Choose your airport wisely. Target Haneda (HND) for all searches. It is located 20 minutes from central Tokyo, compared to Narita (NRT), which is 60–90 minutes away. With kids, the shorter transit time after a long flight is non-negotiable.
Book direct via airline site. Avoid third-party aggregators. Book directly on the airline's site so you can manage your reservation, select seats side-by-side, and request child meals or bassinets immediately after purchase.
Secure bassinet seats early. If you have an infant, call the airline's customer service line immediately after booking to request a bassinet seat. These are limited and assigned on a first-come, first-served basis.
Optimize flight timing. Choose 'red-eye' flights that land in Tokyo in the early afternoon. This allows your kids to sleep on the plane and keeps them awake until a reasonable evening hour in Tokyo, which helps reset their body clocks to JST faster.

Should I pay for an extra seat for an infant?: If you can afford it, yes. Having a 'lap infant' on a 12+ hour flight is physically exhausting. Buying a seat allows you to bring your own FAA-approved car seat, which is safer and keeps the child in a familiar environment.
How do I deal with jet lag?: Start shifting sleep schedules by one hour each day for three days before departure. Once in Tokyo, stay outside in the daylight as much as possible on your first day.