Slaves were often entrusted with the care of the plantation owner's children. Case in point, when Thomas Jefferson went abroad to France as an ambassador after the Rev War, he sent for his youngest daughter, Mary, who was accompanied across the ocean by the slave girl, Sally Hemmings. Sally was only a teenage girl herself at the time but was a last minute substitute for another slave woman who was originally supposed to accompany Mary. Sally is the girl who later becomes Jefferson's mistress and, allegedly, bears him several children. I've not seen a lot of evidence that the "mammy" of the later period existed in the colonial days, but at various times, trusted slave women were indeed put in charge of the children.
Another historic example would be Tituba of Salem, Mass in the late 17th c. She was a Caribbean slave who taught the Paris girls and their friends how to tell fortunes which sparked the notorious Salem Witch Hunts. A peek into these two incidents indicates prior to the 19th c deep south, slave women were sometimes an integral part of the raising of white children.
Exactly! this was a transitional time period, so many viewpoints and lifestyles abounded. Though no matter how characters are portrayed, someone will shake their head and say, "It never happened like that" or roll their eyes and say, "This is all so cliche." You can't win so ultimately do your research and just write the best story you can.
Race and slavery are also such touchy subjects. I'm afraid as I write about it that I'm sure to offend somebody no matter what.
And yes, to what others have said, be sure to keep in mind that there was a major shift in attitudes between the Revolutionary and Civil Wars. However, you might be able to get something out of the antebellum sources listed above. Some of the arguments for/against slavery would have been the same, but maybe employed in different ways by different people.
Speaking of good old Jefferson, he was pretty set against slavery. So were many of the Founding Fathers, even those who owned slaves. They simply assumed that slavery would dwindle and die. Washington freed his slaves in his will, but they weren't to be freed until after Martha's death so that she wouldn't be left with an empty plantation. TJ wanted to free his slaves, too, but if I remember correctly he was so far in debt that he couldn't free his slaves without sending his daughter into poverty.