Just a report here. We ordered the Sentence Family and are using it for the rest of the school year. After the first lesson, he said "Can we do another one? PLEASE??" Wow. I think the only other time I've heard that was when we did Times Tales.
We'll see how the retention goes, but so far the process has been painless. I have him recall the part of speech definition from FLL when we introduce a new character. The other day I printed out a list of sentences and had him underline the nouns and verbs. (Blue for nouns, since "Noun" wears blue, and red for "Verb.") He got them all right, so something must be sticking!
There are some clever ideas in here. Such as the black nose on Mr. Declarative's dog to represent a period, Adjective and Adverb drawing pictures of their brothers Noun and Verb, and the lines of the sentence diagrams becoming the children's beds.