Is it permissible for Muslim children residing in France to eat unslaughtered meat available in schools, knowing that it is not pork, due to the father's inability to provide them with other food?

It is not permissible for children to eat meat that has not been slaughtered according to Islamic law (non-dhakiyyah). If they are adults, they incur sin by eating it. If they are young, whoever enabled them to eat it incurs sin. They must be warned about this, and a halal alternative should be prepared for them. We also note that residing in lands of disbelief can place a Muslim in hardship, so a Muslim should strive to reside in a Muslim country, especially if they have children.