Mr. Oleson and Mrs. Oleson?

This may be an odd question but how did they only have two kids? Did they just no longer have intercourse which isn’t far fetched given the squabbling between them or was there contraception back then? I know there was pills and condoms but I doubt Mrs. Oleson would have been one for them. She mentioned that she stopped at two so how did she stop? Did she go through menopause?