The answer is yes and no. Mostly no. Dictionary.com defines toy this way:

toy (noun)
  1. an object, often a small representation of something familiar, as an animal or person, for children or others to play with; plaything.
  2. a thing or matter of little or no value or importance; a trifle.
  3. something that serves for or as if for diversion, rather than for serious practical use.
  4. a small article of little value but prized as a souvenir or for some other special reason; trinket; knickknack; bauble.
  5. something diminutive, esp. in comparison with like objects.

ThinkBlocks are a "small representation of something familiar". They are a construction set for ideas, with which we are all familiar. But ThinkBlocks are not merely for children. They are used by preschoolers to PhDs and many other types of people. ThinkBlocks are definitely not a "thing or matter of little or no value or importance", they are not intended to serve as a "diversion", they do have a serious and practical use although they are also fun to play with.

By these definitions, ThinkBlocks are definitely not a "toy". Its probably better to call them an educational tool...a tool for 21st Century Thinkers. But if you want to call them a toy, we don't mind. Our first run of ThinkBlocks' packaging and our original website called them a toy, but we found that it was misleading for many of our customers.