Diddy Is Desperate to Speak to Children, Concerned For Their Well-Being

Diddy's not in a good situation right now ... locked up in the Special Housing Unit of a notoriously tough jail -- but, TMZ has learned his chief concern is his children. Sources close to Diddy's family tell TMZ ... Diddy's holding up okay -- given the circumstances -- but he's worrying about his kids from his 10 ft. x 8 ft. jail cell, desperately wanting to speak to his kiddos. We're told people closest to him…