What is the context? Did their father sexually molest them? Did he gamble away all their money so they had to live in the street? He he sell them as child brides? Whatever he did, he didn't allow them to be innocent children, but without context it's impossible to say what or how.
The saying "the best is yet to come" means that good things are in the future.
Thanks very much for your answer. Do you mean if someone does something bad to them in their childhood, like beat them a lot violently or like your examples above, we can say he stole their childhood?
You could. It would apply to things that are likely to have a long-lasting pyschological effect on them. If he just made them do more chores than their friends and not let them watch TV during the school week, it wouldn't count. If they grew up afraid in their own homes, and they had to act like little adults to protect themselves and others in their family, then you could apply that.