Mantra for child good behaviour in Hindu religion is associated with Goddess Lakshmi. It is believed that the rebellious and bad habits of a child can be changed with the blessing of Maa Lakshmi.
Mantra For Child Good Behaviour
ॐ श्रीं ह्रीं क्लीं
श्री सिद्ध लक्ष्म्यै
नम:!
Om Shreem Hreem Kleem Shri Siddhi Lakshmabhaye Namah.
Om Shreem Hreem Kleem Shri Siddhi Lakshmabhaye Namah.
The mantra is to be chanted in the evening during pradosh period. Light a lamp us pure cow ghee and sit facing northeast and chant the mantra.
The child should be asked to read a simple translation of Srimad Bhagavad Purana. This will help in improving the behavior of a child.