We are heading over to Tokyo on July 14th. We have been to Tokyo twice before but during Spring Break (2019 and 2017). My wife and I are going over just to get my 10 year old son and his friend settled for their month long stay to study Japanese. We'll be there for 10 days.

Any ideas on some fun and interesting indoor places (with A/C) to visit? I know we'll have to deal with the hot, humid weather getting to/from the train station from our apartment. Also, how is the weather this summer so far? TIA

If you haven't seen it, the Edo-Tokyo Museum is wonderful and IIRC, it includes a lot of interactive displays that children can enjoy.

baseball at Tokyo Dome

If you want to see baseball in Japan do so. Its a treat. The level of enthusiasm is really cool. I suggest this beautiful outdoor stadium with an old time feel built in 1926.
Stadium Information | English | Jingu-Stadium
Babe Ruth among other hall of fame old timers played there too.