Don't particularly trust Snopes... but the claim doesn't pass the sniff test.
From 1800 to 1860, the black population in the US went from as low as 400K to as much as 7 million depending on who interprets the census. That happened without importation of slaves from Africa. Slaves were treated very different at different times and places. Indentured servitude in which most slaves (including white ones) could earn their freedom was common early but diminished over time. What we recognize is the repugnant, dehumanizing, grotesque treatment of slaves developed as southern settlements moved west and established large plantations. Slaves were very valuable commodities and children as much or more so than adults.
This makes less sense from a purely economic standpoint than a modern cattle farmer throwing a 400 lb calf to the gators.
I can't say it didn't happen... just that it doesn't make sense that it would happen or be very common.