You're assuming the politicians think this will be 100% successful and not, say, 80% successful.

I assume ulterior motives for politicians. It's their PR campaigns that do make it seem like it will solve all children's issues, if only we sacrifice a little privacy for their control. One thing that's never mentioned is increased vulnerability when (inevitably) personal data (of children) leaks.

I think politicians treat IDs as public info. Theirs are, and they have access to a lot of databases of all citizens.