As a school teacher who deals with persistent absenteeism my advice would be to phone and speak to the head teacher, say that "you would never do it again" etc but explain that this is a great opportunity for your kids and that you will ensure that all work missed will be caught up on.
In all honesty unless your children have very poor attendance records the school can't do anything if you do take them out, local authorities etc only step in where children are virtually not coming to school, not because someone's gone on holiday.
I wouldn't worry too much about it. The only exception to this would be if your children are at a private school as they can pretty much do as they please in terms of allowing holidays/dealing with families who go away. In the regilar school system though you will be fine.
Not that I'd be quite so willing to offer this advice to kids at my own school, we have attendance targets to meet you know.....as I am sure your school does