‘Abdu’l-Bahá could have never meant that a child should be left to himself, entirely free. In fact Bahá’í education, just like any other system of education is based on the assumption that there are certain natural deficiencies in every child, no matter how gifted, which his educators, whether his parents, school masters, or his spiritual guides and preceptors should endeavour to remedy. Discipline of some sort, whether physical, moral or intellectual, is indeed indispensable, and no training can be said to be complete and fruitful if it disregards this element.
(Shoghi Effendi, Lights of Guidance, p. 152)

As to your question about the use of physical punishment in child training, although there is a Tablet of the Master which considers beating as not permissible, this does not necessarily include every form of corporal punishment. In order to have a full grasp of the Master’s attitude towards punishment, one has to study all His Tablets in this respect. For the time being no hard and fast rule can be laid down, and parents must use their own wise discretion in these matters until the time is ripe for the principles of Bahá’í education of children to be more clearly elucidated and applied.
(Shoghi Effendi, Lights of Guidance, p. 151)

Bahá’í parents cannot simply adopt an attitude of non resistance towards their children, particularly those who are unruly and violent by nature. It is not even sufficient that they should pray on their behalf.
(Shoghi Effendi, Lights of Guidance, p. 152)

If the slightest undesirable trait should manifest itself, let her counsel the child and punish him, and use means based on reason, even a slight verbal chastisement should this be necessary.
(‘Abdu’l-Bahá, The Compilation of Compilations vol. I, p. 289-290)

It is not, however, permissible to strike a child, or vilify him, for the child’s character will be totally perverted if he be subjected to blows or verbal abuse.
(‘Abdu’l-Bahá, The Compilation of Compilations vol. I, p. 289-290)

Rather they should endeavour to inculcate, gently and patiently, into their youthful minds such principles of moral conduct and initiate them into the principles and teachings of the Cause with such tactful and loving care as would enable them to become ‘true sons of God’ and develop into loyal and intelligent citizens of His Kingdom. This is the high purpose which Bahá’u’lláh Himself has clearly defined as the chief goal of every education.”
(Shoghi Effendi, Lights of Guidance, p. 152)

The Writings are rich in allusions to the individual and his integrity, but also to the social disciplines based upon the moral precepts of the Faith, precepts which each of us must heed lest we fail to reflect in our lives those virtues propounded by the great Teacher for our day, and hence fail to meet our true destinies as spiritual beings.
(From a letter written on behalf of the Universal House of Justice to an individual believer 14 August 1977)

The child when born is far from being perfect. It is not only helpless, but actually is imperfect, and even is naturally inclined towards evil. He should be trained, his natural inclinations harmonized, adjusted and controlled, and if necessary suppressed or regulated, so as to insure his healthy physical and moral development.
(Shoghi Effendi, Lights of Guidance, p. 152)

They must be encouraged and when any one of them shows good advancement, for the further development they must be praised and encouraged therein.
(‘Abdu’l-Bahá, Bahá’í Education, p. 73)

Whensoever a mother seeth that her child hath done well, let her praise and applaud him and cheer his heart.
(‘Abdu’l-Bahá, The Compilation of Compilations vol. I, p. 289-290)

While the physical discipline of children is an acceptable part of their education and training, such actions are to be carried out ‘gently and patiently’ and with “loving care", far removed from the anger and violence with which children are beaten and abused in some parts of the world. To treat children in such an abhorrent manner is a denial of their human rights, and a betrayal of the trust which the weak should have in the strong in a Bahá’í community.
(Universal House of Justice to an individual believer, 4 August, 1996)