Is it permissible to allow a small child to kiss his female friend on the mouth in the nursery?

A child is not held accountable, according to Islamic law, for kissing a female classmate. However, he should not be enabled to do so, in order to accustom him to goodness and virtue, especially in this era which witnesses attempts to invade the minds of Muslim children with alien ideas. For the boy is a trust, and his pure heart is receptive to everything it is inclined towards. If he is accustomed to good, he will be happy; and if he is accustomed to evil, he will be wretched. The father must protect his son from the fire of the Hereafter by disciplining him, teaching him good manners, and safeguarding him from bad company.