The Atlanta Braves 1st baseman was getting in some trick-or-treating with his fam when at one of the houses ... a little boy was decked out in a Freeman jersey, baseball pants and a Braves cap.

Freddie couldn't just let the kid walk by without saying, "hi" ... so he surprised the boy with a conversation and a photo!!!

The scene is adorable ... it took a second for the kid to realize it was actually Freddie (he was wearing a Halloween cap on his head) -- but when he figured it out, it was pretty awesome.

"Are you me?!" Freddie asked the kid. "Are you me for Halloween?! That's my last name and that's my baseball number. Want to take a picture?!"

The little boy said, "of course" ... and the photo will make your heart melt!!!

Props to Freddie for the cool move ... and, by the way, props to his wife Chelsea for always having the camera ready for amazing Freeman moments.

Remember, she was the one responsible for filming Freddie's little son having an unforgettable home run derby just a few weeks ago.