BA - separating children from parents

How does an airline separate a family of four on an overnight flight. Same booking reference. You can't check in online, if you are lucky enough to get someone on the phone they tell you the seats are apart. That's separating children from parents. Even an overbooked airline should have some sort of moral bottom they wouldn't easily stoop below. Especially BA - so called first class? Disgusting behaviour, they should be ashamed.