I took my daughter to Tokyo when she was 4. We stayed in the Sunshine City Prince Hotel in 池代, they have 3-persons room to choose. We have stayed there twice. We loved to stay there because it is clean & the room is relatively big. It takes 10 mins walk to train station and downstair of the hotel is the large underground shopping mall.
My daughter got 流鼻血 easily when she was in Japan in winter. Because the weather is dry & cold outdoor, but very stuffy & warm indoor.