Well this is quite a difficult question to answer. There can be dimensions to it.
It is true that we all learn our first lessons from our parents. They teach us how to walk and talk. It is them who instill in us moral values and etiquettes.
But does this mean that a parent is the child’s best teacher?
Imagine an irresponsible and a negligent mother who does not feel it is her duty to infuse good habits within her child.
Imagine a reckless father who does not punish his child when he steals money or does not scold him when he speaks to his elders in bad manners.
Imagine the parents are illiterate and hence are unable to tell about the dangers associated with electricity, fire, household chemicals or drugs to their children. In such a scenario, the child may cause harm to himself and to others as well.
In the worst case scenario, a parent may instill hatred against a particular section of the society or against people of a particular religion, race or creed. If the child is brought up in such a hostile environment, then he is bound to harm others when he grows up.
Hence one can say that parents are the first teachers but it will be wrong to presume that parents are the best teachers.