Is taking food (such as chips and chocolate) from kindergarten children and hiding it from them considered theft, given that I am a teacher and they are not allowed to eat it?

A Muslim must seek out the lawful in all things, for a body nourished by unlawful means will not enter Paradise.

If items are designated for the kindergarten, it is impermissible to take them without explicit or implicit permission from the authorized entity.

If items are intended to be discarded and spoiled, there is no objection to taking them and benefiting from them, whether with or without the knowledge of the administration, because there is no meaning in discarding them except to permit their use.

The employee is entrusted with what is under his hand, and he is not permitted to dispose of it except as authorized. Otherwise, he is a betrayer of trust and an unjust consumer of wealth, for Allah Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]," and His saying: "O you who have believed, do not consume one another's properties unjustly," and for the saying of the Prophet, peace and blessings be upon him: "The property of a Muslim is not lawful except with his willing consent."