She works in a private school and serves meat to children and does not know the ruling on this

Praise be to Allah.

If you are not sure about this meat and think that it may be pork, then it is not permissible for you to serve it to the children. 

But if you know that it is permissible meat such as beef or lamb, but you are not sure whether it was slaughtered in accordance with Islamic sharee’ah or not, then it is halaal and no attention should be paid to this uncertainty, so long as the one who slaughtered it was one whose slaughter is valid, namely a Muslim, a Christian or a Jew. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: 

If this meat comes from one whose slaughter is permissible, then it is halaal, and we do not have to ask how it was slaughtered or to ask whether the name of Allaah was mentioned over it or not. We do not have to do that and indeed we should not do that, because asking about this comes under the heading of exaggerating about religious matters. Hence when people came and asked the Prophet (peace and blessings of Allaah be upon him), “People bring us meat, and we do not know whether they mentioned the name of Allaah over it or not?” He said: “Say Bismillaah yourselves and eat.” He said not say: Ask them; he said: “Say Bismillaah yourselves and eat.” ‘Aa’ishah (may Allaah be pleased with her) said, narrating this hadeeth, They had recently become Muslim, and the one who has only recently become Muslim may be unaware of the necessity of saying Bismillaah when slaughtering. 

Whatever the case, if meat comes to you from people whose slaughter is permissible – and those whose slaughter is permissible are three types of people: Muslims, Jews and Christians – then do not ask. 

The Jews used to give gifts of meat to the Prophet (peace and blessings of Allaah be upon him) and he would eat it without asking about it. The Jews would invite him to eat barley bread and fat, and he did not ask about this fat and how the animal it came from was slaughtered. The best of guidance is the guidance of Muhammad (peace and blessings of Allaah be upon him). End quote. 

Liqa’ al-Baab il-Maftooh. 

See also the answer to question no. 10339. 

And Allaah knows best.