B.C.
Our son stayed in one center from 3 months old to 3.5 yrs old.
Then he was potty trained and ready for pre-school so he went to a Montessori school from 3.5 through kindergarten (that was the highest grade they did).
Then we did private school for grades 1 and 2 and then we moved 4 hours away and he's been in public school ever since and will start 10th grade in a few weeks.
I have no idea what the circumstances are but the number of day cares your kids have been through seems excessive.
Some of it might be due to with issues of the day care(s) but for that many switches I'd tend to think some of the issues are with your kids.
Is all the switching in the best interest for them?
What sort of stability are they getting?
How can they make friends if they are switching all the time?
Are they having issues that seem to repeat over and over again and are not being resolved?
Only you can answer that one (I don't really what to know what the answer is).
If you have no other options then you'll have to get them a nanny or baby sitter to watch them.