In Osaka I might suggest the aquarium. I am a fan of aquariums and visit whenever we are overseas. I found the one in Osaka quite good.

In Kyoto, your son might enjoy the Sagano Scenic Train from Arashiyama through the mountains to Kameoka in 25 minutes. From there you can take a boat ride on the Hozugawa river back to Arashiyama (about 2 hours).

Have you been to Sea Paradise in Yokohama?

I've successfully purchased tickets for a Yakult Swallows game at the Meiji Jingu Stadium. We will be sitting in the hOme Outfield section. It's for the "cheering umbrellas" does that mean we should buy one of their mini umbrellas?

I also managed to buy myself a ticket for the NHK Symphony at the NHK Hall. It is a bit surprising to me that you have cannot choose your own seat; only the price category and they assign you a seat.

Anyway, both purchasing process was easier than anticipated.

Plenty of fans without umbrellas
[NPB] Went to Yakult Swallows game, this is their tiny umbrella based 7th inning stretch tradition : r/baseball

We went to a game there in 2023, and it was good fun -- even though the home team lost badly. We did not buy an umbrella, but many of the fans had them. There was a band in one of the outfield sections. Someone nearby noticed us and bought us beer!

We are looking forward to it! Should be a lot of fun

Might be the only chance you will ever have to buy an umbrella like that.

Hi Yk! You've received a lot of great info, and now you just need prioritize your "must sees" and those you can drop if the days are too packed.
I have a few tips for you:
1). Check the opening days and times before you head out to the parks, museums, etc. We were in Tokyo in November and a surprising number of places were closed for renovations or had changed their hours or days closed, without editing their websites.
2) In the same vein. check the ferry schedule for the trip up to Asakusa from Hamarikyu gardens. I remember (years ago) when we went to the gardens after breakfast at tsukiji, we didn't need nearly as much time in the garden as I'd planned. The first ferry was a lot later than the park opening, so we had a long wait in drizzling rain before the ferry arrived.
3)A boat trip that I preferred to that one was the trip in Kyoto that someone mentioned above. The Kyoto boat ride was prettier and on smaller, traditional wooden boats. If you don't mind a short bus ride, you can take an old fashioned train to complete the trip to/from Kyoto. Here's a random description https://www.japanrailpass.com.au/hoz...%20reservation.
4) In Kyoto, I highly recommend Sanjusangendo temple. In addition to the statues, it has an interesting history as a place for archery training and contests along the looong side of the building. There is still a very large archery competition at New Years. What my kids loved (and we've talked about it often over the years) is that there are still spots in the rafters where poorly-aimed arrows took out little chunks over the centuries!
5) If you can, take lots of Yen. In the old days you had to carry cash because nobody accepted credit cards. Now, most places accept credit cards, but tack on a 4% surcharge. At least Japan is safe enough that carrying loads of cash is not very risky.
Have a great trip!

"Too late for Sakura/ other garden suggestions?
We won't arrive in Japan until the second half of April. Will there be any cherry blossoms left to see? Unfortunately we are tied by my son's school vacation time. If it's all done by then, what is blooming during that time? I love peonies and have read Hama Rikyu has many peony varieties there. Is April too early for peonies?"

The current (seventh release) forecast for cherry blossoms shows full bloom for Tokyo March 23, Osaka and Kyoto on March 30. I will be arriving in the Osaka and Kyoto area a week later, and hope to catch the tail end of it, but I believe you will be too late.

However, you will be just in time for peonies! Google the best places to view peonies in Tokyo, Osaka, and Kyoto.

I got to Tokyo a couple of days ago and have used my US credit card in numerous places and there has been no surcharge on my payment. There are some shops that ask you to choose between US$ and JPY and you should always chose JPY to avoid extra charges. Of course, this assumes your credit card doesn't have foreign currency conversion fees.

Thanks for all the additional tips and comments. Will delve more into them next week as I gear up on planning details. Friends of ours are currently in Japan for 2 weeks, so I'll also get lots of tips from them when they return (as well as their transit cards).

>> choose between US$ and JPY
called Dynamic Currency Conversion. Always choose the local currency to avoid DCC