A good set of toys that we have at home with significant replay value, because the children pick them up to play with on their own, are magnet tile or tiling toys. There are a variety of toy sets, such as the Magformer, Magna-tiles, Clix, which are all similar (we happen to have pieces from the former two sets) and retail at about US$100 range for a large box set with 100 pieces or so. There are smaller themed box sets with fewer pieces, < 20 pieces in the US$30 range, which is as I recall what we bought as unfortunately I do not have the boxes nearby; some of the themes my children revisit are vehicles and geometric shapes.
The magnets tiles are robust and contain strong permanent magnets that can lift paper clips, attach to refrigerator surfaces (four or five square pieces stacked vertically don’t slide downwards) and be used to probe for magnetic possibilities. These toys also go into bathtubs without problems, though interestingly some of the pieces float while most sink. The sizes are large enough for young fingers to handle with ease.
We introduced these toys to the children when they were as young as a little over one year of age. What is instructive is to see how two dimensional squares, triangles, hemispheres and other shapes can be combined, stacked or organized into three dimensional objects. Now that the older child is nearing five years of age, he has already been creating larger objects, from “houses” to fantastical vehicles. The younger child has also found fascination with these toys, particularly in the wheels, and asking how vehicles make turns.
As the children grow older, I would be interested to find out what other explorations could be possible with magnet tiles, such as how to bring in the concepts of electromagnetism. Also interesting is to continue to explore the cross over between three dimensionality and its projections onto flat surfaces, such as in maps, for example.