I was just thinking and the writers don't mention Sam and Freddie's dads. I thought maybe the two had a bad past that made them not mention them.
Maybe Freddie and his mom was getting physcally abused. Maybe that's why Freddie's mom is protective of Freddie and knew that Sam abuses Freddie playfully or something. I think that once Freddie's dad got arrested and they moved to get away from where they were abused because it would bring up bad memories or something. I also think that it's painful for Freddie to mention him because it hurts or they saw his dad die in front of them or something.
Maybe Sam's dad did a bad crime to get arrested and he made Sam not mention it to the cops. Maybe Sam saw something she shouldn't have and got scared because of it. I think that Sam's dad moved out of the house when Sam and her sister was born because maybe that's why Sam doesn't know anything about him.
Anyway comment me on what you think they don't mention their dads.