Unit blocks are a wonderful developmental toy. Not only do they help teach little ones cause-and-effect as they build, then topple, then rebuild their creations, they actually help teach important math concepts. Two small blocks equal one medium block, and two of THOSE equal one large block. Two small rectangles equal a square. OR two small triangles equal a square. All of these various forms of equivalency help children internalize mathematical concepts. And it's fun! Unfortunately, wooden unit blocks can often be very expensive. Not so with these blocks. These are very affordable. These blocks have now lasted us through children, and are in just as good shape (with the possible exception of a few crayon scribbles) as when we got them.
The only downside is that their crate has a tendency to fall apart. I think we finally had to glue ours.