Bought a size L for my 2.5 yr old daughter, and it fits perfectly, with room to spare. I think she'll definitely get another year out of it. She wore it religiously in the pool during a recent trip to Turks & Caicos, and it completely protected her head and face (sunscreen on her face also) against the incredibly strong sun. It's floppy in the back, but a little more stiff in the front, so it doesn't fold down into her face. I had her in Iplay hats prior to this, but they're terrible with being too flimsy.