What is a good souvenir for children?
Big soft toys! Japan has tons of soft toys that come in many shapes and cute characters. I would recommend you to visit one of the game centers and try out their UFO catchers. In some places like Round One, Namco etc, you can ask the staff how to efficiently win it or place it where you can easily win (maybe within 3 attempts) . These days, soft toys are softer and better than a pillow. Can keep oneself warm!