Ever since I showed him Dora the Explore, Little Guy became obssessed with the show (and the Go Diego Go series) and interested in learning Spanish. I don't know what fascinated him so much but these two shows are his current favorites. Perhaps he can identify himself with the kids who speak (and mix) different languages? I know these shows won't make kids actual Spanish speakers right away but he's learned quite a few Spanish words from the show and always asks "what do you say (so and so) in Spanish?" (and we ask the same question to trusted google to get the answer). They definitely helped him interested in learning Spanish.
Now after learning various Spanish words I feel we're ready to read children's books that are written in Spanish and English together to advance our knowledge of the Spanish language. One of those books I found is called The Moon Is La Luna written by Jay M. Harris.
The book contains several silly rhymes that use a mix of English and Spanish, many of which with the words that sound similar in both languages but mean quite different things. For example, una flor in Spanish sounds like the floor in English. Frankly some of the rhymes didn't quite make sense to me but I found many others entertaining and quite funny. My son's favorites that always induce giggles are: Pies in Spanish are feet! (with a funny picture of a foot and a pie) or the one that writes papá means "dad" but papa means "potato" and it goes "so watch how you say it, unless you would like a potato to tuck you in bed".
Again this won't make you a fluent Spanish speaker right away but it's really a fun book for those who are interested in learning Spanish. It certainly made my son more interested in learning the language even further.