My children are homeschooled at the moment so we are able to take them places during the school term when it's not as busy/things are cheaper. I can see why parents with kids in school want to do that, not just because it's cheaper but it might be easier for working parents to get leave at other times of year. But on the other hand it must be disruptive when they go back to class having missed things and needing to catch up. It's a shame schools can't be more flexible about this stuff, but they do have a lot of material to get through each term.
I think it is best to not interfere in the schooling of a child.
There are enough times they have on school holiday's to have time with them.
In certain cases 'maybe'(e.g. if a overseas grandparent was dying or not many yrs left maybe.)
I think it also depends at what stage in their school life they are at.
You also must remember they have to catch-up, on their return....that is a burden no child should have to face.
I did when a child in Primary School.....it was Huge.Other kids poke fun, and on the whole you feel the 'odd-one-out'.
No child needs that in their lives, it is hard enough for them.
Up to the age of 11, I don't think a week or two missed off school in the course of a year will make any difference to a child's education. Teachers often have training days during term time, when the children get an extra day's holiday - added up that's probably a week lost, so if that's alright then i don;t see what harm a missed week for a holiday would be.
I don't see a problem with missing out on a few days to a week max, but anything longer than that might be an issue. I agree that it is easier to take younger children out of school than older - when exams are near.