As soon as you have kids in the age range where school is mandatory you are pretty much confined to the school holiday roster for big trips. This means you pretty much have to get your planning going soon, if you want trips that are both interesting and possible.

Planning ahead is the only way to actually have some freedom. You can rent really nice cottages, get that night train reservation, etc., as long as you plan ahead.

I'd love it if it were possible to have elective days off for kids in school as well, but that's usually only possible for people in certain jobs who can't use the regular school holidays.