Sammy doesn't do much. Mostly he cries and sleeps, but as time goes on and Dean catches his baby brother staring at him from his car seat or high-chair, he becomes more interesting.
Dean takes care of Sammy. He holds the bottle while Sammy drinks, runs a cloth over him during his bath. He reads to Sammy about bunnies. At least that's what he thinks the books are about. That's what the pictures are, anyway. Dean's favorite part of his story is when the big brother bunny saves his little brother from the farmer. Because that's what big brothers do.