A man watching a 3-year-old boy was busted after he disappeared with the child for 17 hours and took him to a Brooklyn drug den, authorities said.

Larry Fuller, 60, a relative, agreed to baby sit little Shaughn Mack-Cherry at an apartment on West 11th Street in Coney Island while his mom went to work at 1:20 p.m. Friday, a criminal complaint says.

Fuller took the boy to a nearby apartment on Avenue V known for drugs, where he did some himself cops said.

When the mom returned and saw the two missing, she called Fuller at 12:30 a.m., and he told her he wasn’t bringing the child home that night, the complaint states. Fuller was arrested at 6:15 a.m. after police traced his phone to the drug location, cops said.