Louis Tomlinson -- Check Out My Kid ... First Pic of 1D Baby (PHOTO)

Louis Tomlinson just revealed his pride and joy -- showing the world what the 1D baby looks like -- and he's got a name too!

Tomlinson posted the pic of baby Freddie Reign Tomlinson to his Instagram account Wednesday night ... and as you could've guessed, One Direction fans are going nuts. Louis' former GF Briana Jungwirth gave birth to Freddie in L.A. on Thursday and by the looks of things ... Louis is already a hands-on dad.

Jungwirth shared a pic of the kid too.

Freddie's got style.