In All My Sons, Ann says, "I know what I'm asking, Kate. You had two sons, but you've only got one now." What does she mean?
Ironically, it may be possible that Ann is referring to Larry in this comment. Ann says this to Kate before she shows Kate the letter that she received from Larry. So at this point, Kate is still insistent that Larry is alive (with the inner fear that he may have been killed in the war). Ann wants Kate to accept the "fact" that Larry has been killed in the war so that Kate can move on with her life and preserve her memories of Larry as her son. Because Kate cannot let go of Larry, her relationship with Chris has been stressed: Kate has told Chris that he will not marry Ann and she has suggested on several occasions that Ann leave the house. Therefore, Chris is angry with Kate for not accepting his wishes, and he plans to leave the area to start a new life in another city. So in this way, Kate has already lost Chris, but she can still hold on to Larry if she accepts his death.
Ann got a letter from Larry which had his announcement of his death and telling her not to wait for him, so Ann decided to show this letter to Kate to convence her that Larry is dead. Now Kate only has Chris and she should let him live his life as he wants.
Ann is asking Kate to accept that her oldest son Larry was killed in the war. Ann has accepted this (though no body was found) and has since fallen in love with Chris. Because of this, Ann is simultaneously asking for Kate's blessing to marry Chris. Kate thinks if she does this, it will mean she is giving up hope that Larry will one day return and therefore be writing him off as dead.