Final answer:
The expression means parents will face difficulty in controlling a child accustomed to freedom, as the child will likely resist new restrictions, leading to conflict.
Step-by-step explanation:
The expression "Woe to the parent who attempts to contain the child who has been allowed to roam free" means that parents will face great difficulty or distress when they try to impose limits or control over a child who has previously been given a lot of freedom and independence. It suggests that the child used to freedom will resist or struggle against sudden restrictions, making the parent's task very challenging. This difficulty is highlighted in historical accounts and literary works where children, once given freedom or indulged, find it onerous to adapt to constraints, leading to strife and conflict within families.