Amanda Seyfried OMG! Alec Baldwin's Baby Is ...

9/20/2013 4:15 PM PDT

So, Alec Baldwin and Amanda Seyfried run into each other on the streets of NYC ... and she catches a severe case of shock-face -- question is: why?

Here's the scene ... Amanda and her bf Justin Long were walking their dog today ... when they bumped into Alec, his wife Hilaria and their newborn daughter Carmen.

Something happened, or something was said, that left Amanda fully agape.

It could be ... "Wow, your baby is adorable!" 

Then again ... Alec and Hilaria's dog is awful cute too.