There is no biblical reference to support being tough and staunch in order to change the behaviour of a child or an adult or anyone else. It is the power of God's word and the influence of the Holy Spirit, the power in the word which convicts and changes others, not the power of the human personality.
The world operates out of the emphasis of intellectual skills and abilities to reason out the problem, to eventually outwit the child. All this does is to teach the child to also outwit and manipulate the parent.
POWER STRUGGLE-
What follows is the suggestion of 'will-power', one pitted
against another, one trying to control another. This speaks of
witchcraft which in reality is turning over one's will to another
human being, the spirit of Jezebel. The only Person qualified
to change another's will is the Holy Spirit.
HOLY SPIRIT
The only way to allow the Holy Spirit to act in the situation
is for the parent(s) to act in the wisdom, and in the love and
power of God's word.
SIN
Parents and child both are born in sin. All of us have a rebellious
and independent spirit. Not a question of will-power but the question
is one of obedience, the breaking of this disobedient, independent
spirit of doing your own thing. This requires a 100% biblical
approach whereas both the parent and the child are placed in the
realm of the Holy Spirit. Both parties learn to depend on the
Holy Spirit. The parent teaches child to gradually be free of
depending on parents to be completely dependent on the Holy Spirit.
Human reasoning, strength of personality, witty schemes, tricks,
will not do it.
PRINCIPLES
CONCLUSION
Experience as a guide leads to reliance on one's own ability
and intellect to discern problems and the solutions which leads
to manipulation to change the behaviour of another.
Our sole source, and all that we need, is the word of God for
the Gospel is the power of God which changes the hearts, the minds
and the behaviour of man.