Origin of the name "Lastings"?

[Baseball Guru]

So I'm watching the Mets/Dodgers game and Vin Scully (who knows everything) says that Milledge got his name after he was the 3rd of 3 boys and his parents decided he was going to be the "Last" kid, thus the name "Lastings":laff:

[redsfan]

I was wondering where they came up with it when I heard the name