Why should whole families be forced into PR when only one may want it? The UK govt, the Australian govt, indeed most governments, do not insist that all members become PR or Citizens when only one applies.
Ones nationality is a personal choice, and I assume this is why the Singapore govt recognises that children, who do not have the legal capacity to make the decision, can have dual citizenship. They can make the choice when they are older. At times, a parent will also make a decision for a child when they think that they would like to keep their child's options open. Sometimes, it is not for a parent to make hard and fast decisions as to nationality. I know my partner was annoyed by his parents making them emigrate as a family. He at least had the chance to reverse the move as he had retained dual citizenship.
It is simply illogical insist that whole families should be forced into PR or Citizenship because of the wishes of one member. It merely means that some members, who may not wish to be included become less loyal or unwilling citizens and PRs.
The old systems was a good one. Each member of a family could make a choice about how committed they were to Singapore. Those that were not committed, could only stay on short term passes, those who wanted to stay could start the process towards citizenship.
I remember when you could apply for PR before you came to Singapore. This is how it works in most countries when you want to emigrate. But Singapore, is different - perhaps Singapore wants to such and see before it allows you in. They do like to have their cake and eat it too. I would suggest that Singapore has a very different take on immigration/emigration - they seem to see these as fluid.
Most people, who chose to emigrate from their country of origin, chose where they want to go, make and application for residency and then move with the expectation that this will be their home for the rest of their lives. This was the traditional route. This has changed so much in Singapore - less so in the rest of the world. If you chose to immigrate to the UK the Home Office like to think that they are giving you a visa for you to ultimately become a Citizen. Yes, it gets abused, but this is the official intent.
And as a final note, remember that although our host nation professes that it does not allow dual citizenship, there are plenty of Singaporean adults that have it!
so how ?? 
