2 years & up. Combine the energy of gross-motor activities with the creativity inherent in block play using All-Weather Hollow Blocks. Molded from new Poly+ material, the lightweight blocks and planks in varying sizes in this set allow for substantial, interactive group builds in muddy, rugged environments. Each piece features .6 inch thick hollow walls, weather-resistant stainless steel hardware, and soft-touch endcaps that absorb shock as builds are deconstructed during play.