Things are getting so rough in the Big Apple that even toddlers are getting mugged.

A cruel thug ripped a $400 gold chain off the neck of a 3-year-old boy who was sitting in his stroller and being pushed by his mom in Bedford-Stuyvesant in Brooklyn on Tuesday, law-enforcement sources said.

The crook and an accomplice attacked tot Harvey Hernandez in the lobby of his family’s Malcolm X Boulevard apartment building at 11:45 p.m. after following him, his teenage brother and mom Riyana Guerrero home from a Laundromat.

“I was screaming ‘Let go of my baby! Let go of my baby!’” the mom told The Post in Spanish yesterday.

“[The man] didn’t say anything — he just looked at us and laughed, almost mocking us.

“How could he do this to a helpless little baby!”

Guerrero believes that the thieves might have even kidnapped the boy if neighbors, alerted by her screams, didn’t scare them away.

“I just started screaming and fighting with him, trying to get him away from my baby,” Guerrero said of the teenage creep who snatched the necklace.

He and his thug pal had stalked the family back to their home from the laundry, where Guerrero had just finished her weekly wash.

“They were eye-balling them — and the chain,” said one police source.

The duo attacked as the family got inside the lobby of their building, kicking in the door after the desperate mother had locked it.

After neighbors started coming out of their apartments at the sound of the mother’s screams, the crooks fled with the necklace.

The chain was a gift from Harvey’s godparents for his baptism. It has a small medallion on it with the image of hands holding a child.

Guerrero said she’s just happy that she and her children weren’t hurt.

“I didn’t care about the gold; I was just worried about my [kids],” Guerrero said. “It was horrible. I don’t feel safe going out into the street now.”

The mom said her 13-year-old son was “traumatized’’ to the point where he’s afraid to go outside.

“Now, none of us feel safe,’’ she said. “We plan on moving.’’

The chain-snatcher and his pal, believed to both be about 16 or 17, remain at large.

“I just want the police to catch all of them and do what needs to be done,” Guerrero said.

Additional reporting by Frank Rosario