Even so, as parents we must still provide the best education for our children, because it is impossible for parents to educate their children in the wrong things.
Generally, kids learn to imitate their parents, the way they live and follow daily activities. Which makes advice from guardians to offsprings work faster than that of a school teacher. Unfortunately, parental care is rarely reaching to lots of children, due to business and momentary chase by parents for the kids financial needs.
That's right they all need money for bills, and upkeep, but the emotional training that lacks affects how kids understand things in the society. Unlike the child in the Op that asked his dad questions on gambling, others wouldn't inquire, due to the poor conversation in the household. Hence, they'll have little need to bother their dad with a question as that, and go ahead with their decision.
You are right, of course parents will do other activities which aim to meet their own needs such as for school fees or paying other bills, therefore parents do not have enough time to educate or supervise their children with full time all day, but even so parents will definitely give their best and after they give their best then the decision after that is up to the child. Therefore there is a term for parents who have succeeded in educating their children, when the child does something that can be said to be noble.
Also even though they know about gambling or football betting, it is unlikely that they will question their parents, what is most likely to happen is that they will hide it including their behavior that may involve betting, only children who are innocent or honest I will ask their own parents about it.