Some light and easy to carry stuff are the most suitable.
Such like decorative magnets, bookmarks, candies, chocolates are popular souvenirs from Osaka

There are a few coronavirus infection cases in Tokyo. Nobody knows who is the carrier and who contacted who, who been to where, who came from where. If this is just a leisure trip and nothing urgent, just avoid traveling there. Reschedule the trip is better option. Should be responsible to yourself, your kids, and your family. Merely my opinion.