Whilst I agree asking other parents to keep their child out of school is a no-no letting your child take a day off on their birthday is perfectly fine, you are also absolutely allowed to ask your boss for a day off on your birthday, you'll just need to use an annual leave day but letting a child take a day off on their birthday isn't some life lesson and it isn't in contrast with the "real world". Some companies even give you birthday leave, mine does.