It can be a hard thing to teach your child to clean up and pack away his toys after playing. They'll either be too tired, distracted, or looking for something else to do.
If you feel your child won’t listen, “punish” his toys (not him!) for staying out past their “play curfew”. Use any box or plastic container and toss all the toys left out there. Call it the “toy prison”. Tell your child that they can be set free only if he does certain chores in exchange.
Hopefully, your child will lean the lesson and know better than to just leave his toys lying around next time.