Decades ago when my children were little, I remember reading in a book about childrearing by Penelope Leach how nasty measles was, and how even if your child had one of the milder cases and made a complete recovery from it, you should expect to have to spend at least a week and probably more nursing the child through the worst of it - child in bed, properly ill and miserable. Who would want that for their child if it could be avoided? And nowadays, when it's so common for both parents to be working full-time, how would you manage to get that amount of time off between you?