You may want to ask this over on the main board. The moms usually only check there. I know it's confusing since I moved some older threads here! I need to get them into an archived folder!
As to First Language Lessons, I used it with my first-born son, before we had "Little Hearts..." written. I did enjoy the first half of it and felt the last half got long doing all of the preposition lessons. We also discovered that for all the time it took to present the lessons orally over 2 years, there was little retention. We then moved on into "Easy Grammar for grades 2-3" and still no retention. Then, we tried a host of "fun" but not memorable grammar products and my son still couldn't tell me what a "noun" was! This son is very bright, an avid reader, with a huge vocabulary. My methods were not working, and they were taking much of my precious time. We finally did Rod and Staff 4 starting in grade 5 and everything clicked!
With my second son we have done a more Charlotte Mason approach to language arts (copywork, oral narration, CM-style spelling, dictation, and now written narration). We have also added Rod and Staff English 2 once he was in grade 3. He is having great retention is grammar!
So, to make a long story short.... you can certainly use First Language Lessons with "Little Hearts...", but I don't feel its necessary. The language arts in our guides is very CM, with the exception of starting grammar instruction earlier than CM recommends.