There are many reasons people give to not follow the life instructions of the Bible, and or believe it is the Word of God.

Kids will argue slavery was accepted in the Bible and therefore do not want to believe any of it.
Study Slavery
Did God of the Bible condone slavery? This is the main reason kids give for not serving or loving our God of the Bible. There are many things our kids, and other non believers need to explore. The last thing we want to do is put God on trial or reduce Him to our mere mortal level of understanding.
In short, slavery as expressed in Scripture as a whole, was not condoned or a cultural institution that abused a certain race of people as we think of in our early American history, but there were servants. This is a subject that merits additional study with our kids and for ourselves.
Image from Canva Pro