Leaving Tokyo Haneda as I write this....
Tokyo is really a cash city, very few places accept credit cards, unless it’s a chain restaurant, or an upscale sit down restaurant. Cash was also required at the currency exchange at the airports and metro stations. There is a 72 hour unlimited ride on the metro ticket that can be purchased at multiple places around the city and both airports. 15 dollars for adults and 7.50 for kids. These do not work on the JR LINES, only the metro lines. You must show your passport to purchase. We purchased ours at TIC which stands for tourist information center. The Tokyo metro website lists the places you can purchase them. Use the Tokyo metro app to get around the city. There is a metro guide by the metro stations that lists some of the sights. Harajku is a popular place for kids and has lots of little stores and cafes including cafes where you can play with cats and pet owls.
The Tokyo Tower and Skytree are beautiful at night and Ueno is a nice park with a zoo in it. If you fly into Haneda the Keikyu line runs into the Asakusa line to take you into the city, all included in the 72 hour pass. If you stay near a metro station you can pretty much get anywhere. Hope you like fish!