my sister has become a foster mother to a cute little three year old boy. I have been trying to talk…

my sister has become a foster mother to a cute little three year old boy. I have been trying to talk to my sister about punishment to help her but she won't listen to me. She goes from not having any kids because her and husband can't have any and it's only been her and her husband for 8 years and jumps in with 3 year old that has been jumped from person to person and never really had anyone to care about him. I just hope they learn to calm down and not stress so much.