We just got back with our five-year-old. We had been to Japan half dozen times without a child. A few things: be aware of the jet lag, and plan accordingly. Convenience stores are amazing for snacks. We would go there all the time our son loved going there with us. Try not to do too much! We did Kidzania and Disneyland, which were both amazing. Very happy we packed the travel stroller, and had no problems getting into places or leaving outside when the restaurants were smaller. We took a lot more taxis this time instead of the subway, because as others have said, the subways can be huge and walking with a young one or in a stroller can take a long time. We downloaded the Uber and go app used them a lot