What is the age at which children—boys and girls—are permitted to play together?

It is permissible for children who have not reached the age of discernment (under seven) to mix and play together. However, if they reach an age where there is a fear of lust being aroused or mischief occurring, then they must be prevented from mixing. Imam Al-Shafi'i was of the opinion that a boy is to be treated in three stages: the first is that he does not comprehend what he sees, in which case it is permissible to uncover in front of him; the second is that he comprehends what he sees but without lust being aroused, in which case he is treated like a mahram; and the third is that lust is aroused in him, in which case he is treated like an adult. The Permanent Committee for Issuing Fatwas in Saudi Arabia recommended preventing boys and girls from mixing from the age of seven and above, because it is the beginning of the age of discernment, and as a preventative measure to block avenues leading to evil and corruption.