If you are teaching these children outside of regular school and you do not have any authority over them with regard to their grades or their passing or failing, then there is nothing wrong with you teaching them in their homes and the gifts that they give you are also permissible, whether they are in the form of food or other things.
But if you are teaching them in school, it is not permissible for you to accept these gifts from their mothers, because that comes under the heading of bribes.
Shaykh Ibn Uthaymeen (may Allah have mercy on him) said:
It is not permissible for the teacher to accept a gift from the student, because this comes under the general meaning of the hadeeth narrated by Ahmad in al-Musnad: Gifts to workers are ghulool (wealth stolen from the war booty or the bayt al-maal of the Muslims). And because gifts create love, as it says in the hadeeth: Exchange gifts with one another, you will love one another. And if the teacher's love for this student increases, there is the fear that she may show favouritism. So the teacher has to refuse the gift and say: I cannot accept it.
End quote from Liqa' al-Baab al-Maftooh, 225/16
The scholars of the Standing Committee were asked:
I am a teacher in a school for eradicating illiteracy. Halfway through the school year, when the results are done and certificates are distributed, I receive a number of gifts which I accepted after they insisted and threatened to become upset in some cases. What is the ruling on that? Is it permissible for me to accept them? Is it is regarded as a bribe?
They replied: Giving gifts to teachers in regular schools - government schools or otherwise - comes under the heading of bribes and it is not permissible to give them or accept them.
The Prophet (blessings and peace of Allah be upon him) forbade gifts to workers. It is narrated from him in a saheeh hadeeth from Abu Humayd as-Saaidi (may Allah be pleased with him) that he said: Gifts to workers are ghulool (wealth stolen from the war booty or the bayt al-maal of the Muslims).. Narrated by Ahmad and others.
End quote from Fataawa al-Lajnah ad-Daa'imah, 23/582-583
See also the answer to questions no. 83590 and 82497
And Allah knows best.
Reproduced from Islam QA