How should I treat my baby's sunburn? There's no blistering.

Cool soaks. Soak some washcloths or small towels in cool water and apply them frequently. For a baby, there's not much else to do except wait it out. The involved skin will peel as it heals - that's normal. But please learn a lesson from this and apply a good broad-spectrum sunscreen to your baby (and yourself) whenever you go out in the sun. If you're out there for awhile, reapply it frequently.