They brought the curse on by their choice of disobedience. The curse of Adam and Eve is original sin. No parents with minds corrupted by sin could raise children without infecting them with the corruption. Original sin is like a genetic virus, spread though all of us by the choice of these early parents. All sin requires a consequence.
Consequences are the natural result of misbehavior.
When a child misbehaves, the parent must provide consequences that the child can learn from. Man s consequence is having to toil for a living. In the garden, he would not have had this burden. The burden is the reminder of the consequences of disobedience. It is the reminder of the pain of sin.