Police arrested a Brooklyn man whose 3-year-old grandson went missing after he fell asleep on a train, cops said.

Wiley Reynolds, 49, was picked up in Queens Saturday around 10:30 p.m. and charged him with failure to exercise control of a minor, cops said.

Reynolds fell asleep on a northbound F train Friday evening and discovered his grandson, Kah-yon, missing when he woke up in Queens, cops said.

Reynolds reported the boy missing eight hours after the boy was last seen, cops said. This was a factor in pressing charges against the grandfather, sources said.

The boy was returned to his Newark, N.J. home after another passenger found the boy, cops said.

The boy is unharmed.