When we consider cardboard as an alternative sustainable material, many would compare it with plastics. Mainly plastics that are used for bottles and other cheap and recyclable solutions.
There has always been controversies and issues over how safe are plastics especially after the various treatments and processes it gone through upon the recycling process and also manufacturing. In actual fact, both cheap materials Cardboard and Plastics are not actually cheap. The process to create and recreate them are perhaps not that cheap and easy. On the few previous posts, Plastics have to go through around 6 process during recycling whilst cardboard only one. Thus giving Cardboard a winning factor over its economical aspect and not forgetting that it is much more safer and easier to handle than plastics.

Some suggested solutions that i could work on for my target users *children-preschoolers (as researched previously)
-interactive modular playhouse that could be formed and fixed into some other small furniture
-mutli-function small furniture (detachable forms could be play around by kids like building blocks, to make some other forms etc.)
-push cars
-play kitchen
-study/play table, writing board and storage box all in one
apart from usable products for kids maybe it could be a learning tool for kids too…
eg. learn to recreate creative forms from the modular parts of the furniture
or
eg. learn to organize things, toys into the storage furniture

For now, i am still going to research on plastics and the issues so i could justify my material choice (cardboard) over it.
For the packaging design structures examples, i found a book in the library which shows several complex examples and its templates. I would try to experiment them on cardboard.