The Oso books by "Barefoot en Espanol" are awesome for vocabulary building! These simple books work well with younger kids to introduce them to a variety of topics like days of the week, places, profession,etc. Here is a list of the books available and the topics they cover.
Bear in Sunshine/Oso Bajo El Sol (Weather, Seasons, Favorite Activities)
Oso en la Ciudad (Places, Days of the Week)
Oso En Bicicleta (Places, Transportation)
Oso En Un Cuadrado (Shapes, Colors, Counting)
Oso en el Trabajo (Professions, Places)
Bear at Home/Oso En Casa (Rooms and Items in a House)
Bear's Busy Family/ La familia ocupada de Oso (Family, The Five Senses)
Many of the books at the end have a picture review of the vocabulary and/or a list of key words. Like for example in Oso en Casa there is a floor plan of the house.
Or a review of shapes and colors in Oso en el Cuadrado...
Great little books for language learning!