Police declined to say whether the grandparents would face charges, citing the ongoing investigation.
Landers' mother, Lisa Harter, was "jumping up and down for joy" when investigators told her a few days ago that her son had been found, her husband Richard Harter told The Associated Press in a telephone interview.
He said his wife is "the happiest woman on earth."
Harter said he and his wife were working with an attorney and hoped to reunite with his stepson soon. Police said Landers is married and expecting his first child.
Harter declined further comment and referred questions about the case to his attorney, who didn't immediately return phone messages Thursday. Investigators declined to release the names under which Landers and his grandparents had been living.
Police said the boy's paternal grandparents, Richard E. and Ruth A. Landers, abducted him in July 1994 because they were "upset over pending court proceedings" regarding his placement.
Police spokesman Sgt. Ron Galaviz said it appears the boy's father was never in the picture. Lisa and Richard Harter had married a year earlier.
Authorities believe the grandparents took the boy from their home in Wolcottville and fled. They were charged at the time with misdemeanor interference with custody, which was bumped up to a felony in 1999. But the charge was dismissed in 2008 after the case went cold.
Investigators reopened the case in September when Richard Harter turned over the boy's Social Security card to an Indiana State Police detective.