The inferno at Tyreek Hill's mansion on Wednesday was caused by a child playing with a lighter ... this according to officials.

A spokesperson for the Davie Fire Department in Florida confirmed to TMZ Sports that investigators believe a youngster inside a bedroom at Hill's Southwest Ranches home started the blaze.

It's unclear if the child is related to Hill or how exactly it was able to ignite the flames -- though according to the DFP rep, because officials formally identified it all as "accidental," no further investigations are taking place.

As we reported, firefighters were first notified of the flames at around 1:50 PM ET ... and a short time later, they were able to knock down the blaze with a water hose.

Officials say, fortunately, no one was injured.

Hill was at Dolphins practice when the fire first broke out -- and, according to the team, he left early to handle the issue. He was seen on the scene at around 3 PM ET with his wife looking concerned as he watched officials try to contain the blaze.

Drew Rosenhaus -- Hill's agent -- said, though, in an interview with 7News that his client was in good spirits despite the situation.

"It is very difficult for anybody, obviously, to have your home catch on fire," Rosenhaus said, "but Hill was handling it with as much poise as you can hope."