"That children should learn (foreign languages) orally by listening to and repeating...words and phrases...that they should learn a few -two or three, five or six -new...words daily and that at the same time the old words should be kept in use..." -Charlotte Mason, Home Education, Vol.1, p. 80.
Using the Montessori method (which, interestingly enough, is just like the discrete trials of ABA) can be a very effective way of teaching foreign language to young learners because it keeps the stress low and insures success. (Powerglide Spanish Junior uses this method.) Charlotte Mason began teaching a foreign language with vocabulary, adding about six words a day until the child could begin to read some simple books in the foreign language. They memorized verbs but they were learned in the context of sentences. Then grammar and new vocabulary were learned just as they were in English.
Beginning with one vocabulary word, place a picture of it on the table. Then ask the child to point to this word. (For example, if the vocabulary word is roca or rock, put a picture of a rock on the table (or a real rock) and say, "point to roca.") Obviously, since there is no possibility of error, he answers this first request correctly. Now, building on this, teach a second word, and place pictures of both words on the table. There is a small margin for error now, and will most likely get this one right as well. You can teach the six vocabulary words in this way, always going back to what they have already gotten correctly or eliminating choices if you begin getting incorrect answers. The goal is having them memorize the words by the excitement of success.
You then can begin incorporating them into tiny little stories, substituting the new vocabulary words for the English equivalents. Using the vocabulary not only helps to cement it into the child's mind but also helps them to remember them, even if they temporarily forget them, because they can figure them out in context. (This is how we learn our native language as small children.) We practiced our new vocabulary words in a small story about getting rocas in zapatos (shoes) after a walk in las montañas.