I didn't even do a reception year when I was at school, because I'm an August birthday - and many countries don't even start formal education until the children are 6.
This is a long and very tiring term, add to which the excitement of Christmas = some out of character behaviour, tears etc. I certainly see this in my year 2 class, and many parents have mentioned behaviour at home being bad when I know they are angels in class.
I can't see anything wrong with occasional days off for tiredness, would def prefer this attitude to that of some parents who send their child in on death's door with some calpol and expect us to look after them!
IME (12 years) no-one in reception has had a regular, fixed day off and I can see, from the school's point of view, why it could be hard to manage, but I suppose as long as you don't mind them missing certain areas of the curriculum and having a shorter report/parents evening, being missed out of the class assembly, trips etc then it shouldn't really matter. Or pay for private nursery care which may have more flexible hours, I'm not sure.
Callisto the poor sods 'bloody teachers' are tax-payers too and not your employees. They are just trying to do a very tough job so maybe try and see it from their side? There are a million things to think about and plan for a class and having some children regularly missing does add to the pressure I'm afraid. I DO see your point but maybe take it up with the government?