In your situation I wouldn't hesitate to switch boarding passes around among the kids to group them together the way you want them to board the plane, especially if you end up with large gaps between the boarding numbers. That should alleviate your concern about the 9 and 11 year old being in the terminal by themselves at the end. Checking in that many people it's possible you will have a surprise with boarding numbers.
Anecdotal evidence suggests this plan could be a little more challenging if you're flying into Orlando due to the larger number of families and EBCI's purchased. Heading to the back of the plane is really good advice.