Perspective
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
( Prov. 22:15 ) Folly is in the heart of a child, the rod of discipline drives it out. To reject counsel of the parent who is responsible to God for training the child, the child would be the greatest of fools. ( Prov. 19:11 ) A wise man restrains his anger. He applies patience, overlooks offenses, even for a child, that is, don't be a nit-picker by being on the back of the child all the time.
( Prov. 16:23 ) A wise man's heart guides his mouth, and his lips promote instructions.
( Rom. 12:9-21 ) These truths apply to the child as well as to your peers. As you follow Rom. 12 , not only will the child be trained to be conformed to Christ but the parent as well.
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.