I would agree with the PP. Here is the thing, they are kids! As a former guidance counselor and parent who has pulled her children out of school for the past 7 years during September (by the way, the perfect time to go!!), it just won't count. Sure they might have unexcused absences and/or they might not pull the A with having missed a week (although my daughters always managed to do so), but the truth is, no college, no person will know. Nothing truly matters prior to high school. Unless they are a weak student who can't take the make up work and missing some content, this week is about being together as a family, having fun and having a memory that will last a lifetime. The grade they get in 4th grade, heck in 8th grade won't be seen by anyone but you. Now high school is a different matter which is why, for the first time, we having to travel during the Thanksgiving season (which is not my first choice by any means--way too crowded). As we travel when Disney has
free dining, we have always gone since my girls we 5 & 7 during September. Not only is it free dining but it is the perfect time to go. If you plan it about a month after school starts, the kids have a chance to get acclimated to school but since much of the beginning is review, they are not hugely into new content. I did as a PP did and just let the school know well in advance (not even trying to make it an educational experience) and the teachers all seemed very wiling to get me make up work ahead of time or allow my girls to make up stuff when they get back. For our 8th grader last year, she did bring some work with her and did it on the day we sat poolside.
Another reason September is great is that the weather is still wonderful for swimming which my girls loved and the crowds are super low. We always traveled the 3rd week of September. I am truly not looking forward to the November/Thanksgiving crowds but as I previously stated, once they are in high school, it's another story. EVERYTHING counts!
Again, i don't know your school system and or policy but my thought was always, whether excused or unexcused, it is well worth what this trip has meant to our family and the memories it has made. Only you can determine that for your family. Oh, and I will say that there was that part that worried that with 5 days absent (we took a 9 night vacation with both weekends included), that one of my daughters could get sick and miss enough school that there were consequences like making it up in Saturday school etc but by the grace of God, that has not happened.
I say, pull your kids out when it is best for your family and don't worry about the other stuff. It will be okay. When your kids are applying to get into Duke or Harvard, how they did in 4th grade will never be seen!

Hope that helps give you some perspective to a rebel parent who has pulled her kids out 7 years in a row but who can also look back at 7 incredible and not crowded with free dining vacations!!!