The Horn Book, a publication about books for children and young adults, has published a long list of recommended summer reading from picture books to books for young adults. All were published in 2012 or 2013. For first and second grade readers, the Early Readers and Young Fiction category may be especially helpful. There is a list of books and description for each one here.
Some of the featured books have been reviewed here: The One And Only Ivan, This Is Not My Hat and That Is NOT a Good Idea! Even more are in my to-review or to read pile: The Dark, Who Could That Be at This Hour?, Three Times Lucky, The Great Unexpected and H.O.R.S.E: A Game of Basketball and Imagination. I have also been meaning to read at least one of the Bink & Gollie books because they are co-written by Newbery Medalist Kate DiCamillo and Alison McGhee. Bink & Gollie: Best Friends Forever is on the early reader list.