The Okumusashi region, not far from where we live, is an easily accessible area not far from Tokyo with lots of trails among low mountains and hills. It's great for a family hike and there's rarely a need for snow gear, even in winter.
On Monday, we went with a few friends and were able to to a bit more rugged of a hike than we had ever done there before. The kids held up great, and Tomomi (now midway through pregnancy) was a trooper. We had a great time, even though the cedar pollen set my nose and eyes a-running.
The trail-head is just a ten-minute walk from Ogose station. To get there take a Tobu Tojo line express train from Ikebukuro. Transfer to the Ogose line at Sakado station and go to the end of the line (700 yen one way). Hiking maps are available for free at the station and there are courses for the casual and ambitious hikers. We didn't see any decent stores so be sure to pack a lunch. Ogose is famous for plum blossoms. They are in full bloom right now!