Play and Grow is an amazing blog by a Russian architect that has a passion for making handmade cardboard toys for his little girl. The site is filled with great diy tutorials for upcycling cardboard into early learning toys.
A few favorites:
DIY Geometric Sorting Board (view tutorial)
A cardboard version of the classic geometric sorting board.
DIY Developmental Toy (view tutorial)
An early learning developmental toy made from a diaper box, knitting needles, a doorstop, and paper.
DIY Steamship Pull Toy (view tutorial)
A cardboard pull toy made from a diaper box.
DIY Cardboard Train (view tutorial)
A cardboard train made using a diaper box and boxes from old toys.
DIY Mini Geoboard (view tutorial)
A cardboard version of the classic peg/pin board toy used to make shapes, patterns, letters, etc.
Visit Play and Grow for more cool projects & tutorials!