Recently I have been reading Sandra McKay's Assessing Young Language Learners (2006)which gives an excellent background on the characteristics of young learners, relevant second language acquisition theory for teaching young learners, and an overview of Bachman and Palmer's theory of communicative competence (I have not gotten to the part about assessment yet).
First, Mckay discusses Skehan's (1998) cognitive theory for SLA. Skehan hypothesizes that learners first primarily rely on chunks or formulaes to communicate in the language. Examples of a chunk would be "What's that?", "How are you", "Can I have a ~?". Rule-based learning follows formulaic learning in that learners learn the rules that govern the chunks. For example, "May" can replace "can" in "Can I have a~" or that "Can I have a ~ " is formed by adding the auxiliary "can" to the verb "have" and then inverting it with the "I" (Wow, sounds really difficult, doesn't it?).
On a personal note, when I first came to Japan I spoke no Japanese and to survive in the country I learned essential formulaic phrases such as "Toire ha doko desu ka" (Where is the bathroom?), "Dozo yoroshiku onegaishimasu" ("Please be nice to me" - something that is said all the time here after you meet somebody). About 12 months after I learned "Dozo yoroshiku onegaisimasu" did I realize that "yoroshiku" was an adverb form for the adjective "yoroshi" (fine, nice, good) and that "onegai shimasu" was a honorific form of the very "negau" (wish) and started to use these two words in various contexts.
What I am trying to say is that perhaps the role of grammar is to help us manage, manipulate and make sense of the language we already know rather than to manage and manipulate language that we do now know.
It is my opinion that English picture books supply children with a wonderful opportunity to learn formulaic phrases. Many picture books tend to repeat the same phrases, for example, the "very hungry catepillar". It has been recommended that when reading a picture book with repretitive phrases, that the teacher have the children say the phrase when is appears in the book.
One thing to keep in mind, though, is that Monbukagakusho is proposing to introduce English activities for the 5th and 6th grades. I think that a book such as the "Very Hungry Catepillar" would be too childish for fifth and sixth graders.
McKay (2006, p.37) writes that "Foreign and second language learners who have had little opportunity to draw on formulaic systems developed through language use opportunities quickly become tongue tied and anxious as they try to construct a sentence based on the rules that they learned." In other words, if we have to apply rules every time we use a language the mental burded is so great that we will struggle to say much of anything.
Monkasho has said that it wants Elementary school English activities to serve as a "base" for junior high school and senior high school English. The Japanese junior high school English syllabus seems to be centered around learning grammatical rules. Using picture books, children can learn formulaic phrases which might eventually enter their lexicon. Perhaps, then, primary school English can serve as a base by helping children to learn some formulaic expressions so that when they enter junior high school the grammarical rules they learn can be used as tools to help them manipulate and make sense of the language that they already know.
Perhaps, when we emphasize grammar students get the mistaken impression that speaking a foreign language constitutes applying grammatical rules to every phrase that they utter. Using English picture books might help give children a different view of language.