Playfoam 20-Pack

Loaded these into a small bin for my kids and they've been at it for hours without a single "I'm bored." The best part is that it never dries out, so the half-finished blob from yesterday is still squishy today.

Twenty little foam bricks sounded like overkill until I realized they never dry out, so there's no scrambling to reseal anything. My son built a whole dinosaur, squashed it flat, and rebuilt it as a spaceship in one sitting.

My kids have been squishing these into animals and then smashing them flat again for weeks now, and the best part is they don't crumble or leave bits everywhere. Even after being left on the floor overnight, it's still perfectly moldable.