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

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

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