What is the ruling of the Sharia regarding the desire of a boy under the age of fifteen to sleep in his grandmother's embrace between her breasts, and is that forbidden or permissible?

It is not permissible for a mahram (definition) to look at his mahram women except for what is usually apparent from them, such as the hair, neck, hands, and feet. It is forbidden to touch what it is forbidden to look at. It is not appropriate to embrace a mahram or sleep in her embrace, as this can arouse desire and expose one to temptation. Children must be separated in their beds when they reach the age of ten. Allah has commanded children to seek permission before entering rooms at certain times so that their eyes do not fall upon awrat (private parts) that might arouse their instincts. Therefore, one must avoid sleeping with the grandmother to protect both parties from temptation.