Slaves could lead very productive and meaningful lives. It was not uncommon for slaves to be freed and made a citizen. Some slaves also held high positions (eg. Dentists, accountants, etc). I also understand that the word slave was interchangeably used with the word family.
Sources: https://en.m.wikipedia.org/wiki/Slavery_in_ancient_Rome
And Mary Beard's Meet the Romans (an exceptionally good documentary from BBC. Mary is one of my favourites).
Mary talked about a wealthy Roman woman (a business owner) who freed her slave and married him. Depending on who you ask, her slave would have been considered a sex slave before they married. The truth is always a matter of perspective!
Having said that, the Spanish and Italians used boys as young as 6 as slaves for mining silver and malachite. The boys that survived were significantly physically deformed by the time they reached adulthood. There is also significant discussion about little girls who were forced to play with dolls to be good slave housewives (the girls were described as having terrible lives).
Source: Mary Beard's other Roman documentaries and the history of Sicilian mines (can't remember the link, but easily found on Google).
Trivia: the silver was mined for coins!