At approximately 3:35 p.m. Thursday, Parx Casino security noticed a Ford Explorer parked illegally in the lot. They then observed the grandson in the passenger seat.
60-year-old Alexander Salter Jr. was charged with endangering the welfare of his 12-year-old grandson.
The police investigation found that Salter parked his vehicle at 3:05 p.m. and entered the casino.
After playing slots, he left the building and returned to his vehicle at about a half hour later.
Police say outside temperatures were estimated in the low 90's today and the vehicle was parked in the sun.
The defendant was interviewed and admitted to leaving his grandson in the vehicle for what he believed was 15 minutes.
Salter was arraigned and released on $25,000 unsecured bail.
In August, the state Gaming Control Board, after a handful of such instances, warned the casino to do a better job of addressing the problem. Parx Casino officials have said they have taken steps such as adding more parking lot patrols during busy times.
"Our security is top-notch and constantly patrolling the parking lots to identify something like this. We act immediately," spokeswoman Carrie Nork Minnelli said. She added that players involved in such incidents are permanently banned from the casino.
The Associated Press contributed to this article.