Three weeks into the new year, Sony Pictures is in an unfamiliar position: first place.

After a dismal five-year run, Sony’s motion-picture business has outgrossed all competitors so far in 2018 thanks to a smash-hit sequel to a 1995 family film.

“Jumanji: Welcome to the Jungle” is No. 1 at the U.S. box office for the third weekend in a row,...