Flying in business/1st doen't exclude you from minors because they are entitled to fly in this class too.
Smith
I don't remember the last time I travelled in Business Class where young children were present, that isn't to say that they were not there it's just that most parents are able to control their children by keeping them occupied. Travelling with children over the age of 3 should not really be a problem as they can be occupied, under 3 is more difficult and should you come across parents with such children instead of scowling at them or suggesting a kind of 'airline apartheid' you should try to help them, like most people do. Often, people travelling with young children are doing it out of necessity and not through choice.
The only time I do get annoyed is when older children run amok in the cabin because their parents can't be bothered to control them, though the Cabin Crew are normally good at dealing with such problems.