Disclaimer: My DS is 1st grade equivalent, and I'd classify us as very relaxed, eclectic homeschoolers. Pro tip: never mention the term "unschooling" during your school district reviews. They've had too many people claim to be unschoolers who were really being negligent parents, so the term has been poisoned.
What I've learned from our two reviews last year: It depends on your school district, and on the actual person you get as your reviewer. At your review (it sounds like maybe you already had it for the first semester and are looking for tips on improving the second semester review?), the school district person (we've had retired teachers as our portfolio reviewers) has a form to fill out that's divided by subject. So to make it easier on them (they only allow 15-20 minutes per child), it helps if you have your child's samples divided by subject, too. I like to use a big binder, but you could use any organizational system that works for you--they just really, really, really want to see about 1 sample per subject, per week, per child (or in the case of my DS who doesn't do anything on a regular schedule, I just brought in the entire math workbook even though not all pages were completed). The reviewers we've had love worksheets as visible, tangible proof of the educational process (both that the child has been exposed to a concept, and that they're practicing it, too). However, my DS isn't a big fan of worksheets, so I just take pictures whenever he incorporates words in his artwork, and it counts as both art and language arts (I print them out wallet sized, 9 to a page, and file them by subject just before our review). Most of our binder is made up of my handwritten logs of what we've done on any given day (but it's not uncommon to have gaps of several days between entries for some subjects). I have different sheets for each subject, and for each entry I note the date, time spent on activity, and give a brief description of what happened. But you don't have to make a daily log; it's just that for me, doing it every day makes it more routine so I'm less likely to forget something.
This website is the MD state curriculum. Click on the subject, then on K for kindergarten curricula guidelines, but try not to be intimidated by all the abstract language. Usually a single activity would cover several different goals, so it's really not as overwhelming as it can initially seem. It's set up for the entire school year, so you have until May or June (depending on when your final portfolio review is scheduled) to cover all that stuff (and actually, since you're homeschooling, you're not on such a strict schedule if you don't want to be). However, if you think you'll be entering your kids into the public school system at some point, this state curriculum should give you a good idea of what your kids would be expected to know for any given grade level.
Maryland's big thing (or at least my district's) is "regular, thorough instruction." On my county review form, it lists each subject (and the same form is used K-12): Language Arts, Mathematics, Science, Social Studies, World Language, Art, Music, Physical Education, Health; then there's a column for course content where our reviewer made note of what sorts of "proof" we had--photos of DS doing educational things, writing or art samples, or just a brief list: Legos and board games (under Math). Then there are columns for Reading Materials, Worksheets, Workbooks, Assessments, and Writing Samples. If we brought in any of those, there's a check mark for that subject. If we didn't, it was left blank. Then there's another column called Curriculum Materials. If you're using a particular series of workbooks or textbooks, magazine subscriptions, or a DVD series (Highlights, Click; Sid the Science Kid, Bill Nye Science Guy) that would be noted here. We didn't have much of a formal curriculum for DS last year, so the reviewer just made brief lists of things we did to focus on certain areas--Social Studies had Jamestown listed b/c we'd taken a family vacation there and toured the re-created settlement and museum (and we had pictures to back that up). The final columns are Yes/No: Evidence of regular, thorough instruction.
In your case, since you're using workbooks, bring the workbooks. Or if it's a ton of workbooks, bring in one in the series, but have a list with the full series name/author or publishing house. Or, since you've got twins, if you're photocopying the pages (two copies of same page for each kid), bring in a few of the worksheets along with the list of workbook names. You don't need to prove you've taught every single math skill, but a couple of samples of their work doing addition, filling in missing numbers in a sequence, or sorting or identifying shapes would be fine. They're most concerned that you're not claiming to be a homeschooler while actually not bothering to teach anything at all. They love to see motivated, enthusiastic students, but they'll be almost as happy to see motivated, enthusiastic parents--when the parents are excited about learning, it helps set a positive tone for the kids. You don't have to document everything, but you should be able to verbally fill in any gaps in your documentation (give examples of activities or learning opportunities), and definitely put some emphasis on field trips (even if it's just the zoo, aquarium, or a random museum, it counts!).
Hope that helps!
