Aussies teach children a little ditty to remind them about safety called Slip! Slop! Slap!: slip on a shirt, slop on sunscreen and slap on a hat. (It was recently expanded to include seek and slide, but that's just way too damn long.)
I think that song every.single.time I put my hat on before I go out in the sun. It works for 3 year olds AND 30 year olds!