I have never heard this topic mentioned in a khutbah or taught about in seerah classes I have attended. This is such a shame, over the years so many brothers I have known simply refuse spouses because they do not want the hassle of another mans children. AstaghfiruAllah! But are very happy to follow the Sunnah and marry second wives ....this needs to addressed!
An aspect of RasulAllah (sallAllahu 'alayhi wa sallam)'s life that very few people even think about is that he was a stepfather - a man who raised the children his wife had from her previous marriage.
Many cultures warn men against marrying widows or divorcees with children; insinuations are made that she could never be truly devoted to her new husband if she has her own children to care for. A bizarre, unhealthy rivalry is set up between the woman's child and her new husband.
When the Messenger of Allah (sallAllahu 'alayhi wa sallam) sent a proposal of marriage to Umm Salamah (radhiAllahu 'anha), she told him, "I am a woman with many children!" His response was, "And I am a man with children as well. Your children will be mine."
Umm Salamah had several children by her previous husband, Abu Salamah (radhiAllahu 'anhu), who had died from his war injuries. She was either pregnant, or had just given birth to her daughter Zaynab, when her husband died.
Zaynab bint Abi Salamah (radhiAllahu 'anha) thus grew up with RasulAllah as the only father she truly knew. He, in turn, loved her as his own child. When RasulAllah would come to Umm Salamah's house, he would immediately ask for young Zaynab; he would play with her often.
Zaynab's uncle, Ammar, used to say, "She was the one who has come between RasulAllah and the rest of his family!" - meaning that he would spend a great deal of time with her.
Zaynab bint Abi Salamah (radhiAllahu 'anha) grew up to narrate many ahadith, in particular from her mother and from the other wives of RasulAllah (sallAllahu 'alayhi wa sallam). She also became known as a great jurist of Madinah, and was referred to as the most knowledgeable woman of her time.
From The Salafi Feminist