You can go to a shop called "akachan Honpo". This shop sells all kinds of baby stuff. The most important issue is all items sell in a discount price. I bought all baby things in this shop every time I go to Japan.
You take the JR and take off at 「錦糸町」駅北口, then turn left and see a building with Seibu or Mitsubishi Supermarket on B/F. The shop is located on 5/F.
If you want to know more, please PM me.