Some people are lucky enough to be able to take two holidays a year. This is often done when people have children as they want to be able to have a holiday that is focused completely around the children and what they want to do and then a holiday that is aimed more at the parents.
Obviously this does usually cost more than having one break but if you can take book a holiday for the parents outside of school holidays then there are some great savings to be had.
Other families chose to always go away as a family, believing that a holiday should be for everyone. They may split their time doing some children based activities and others more for the adults. If you wish to go on one holiday for all, then you could look at what holiday clubs are available for the children at your chosen destination, so everyone gets a bit of time to themselves.