At some point the tax laws changed. The IRS started requiring a SS# for every child you deduct on your tax form. That is why kids get a SS# right away, so you can get your tax deduction/credit. I do not know when that started.
This is interesting. The law wasn’t changed until 1986. They must have started handing out the forms in the hospitals prior to the change in anticipation of it. I remember a hullabaloo about it, but I didn’t really remember the details (I was not particularly political at that time, a little too busy with 3 little boys). At that point (1986) they began requiring children over 5 to have a number to list on your tax return, and then in 1990 they lowered it to one year of age.
Hmm... At any rate, the Wikipedia article (I know I know) states that most people did NOT have SS numbers until about age 14 before that.