The Prophet, sallallahu ^alayhi wa sallam, praised the Arabic language and ordered that we love it.
The Arabic language is the language of the inhabitants of paradise and is the first language that Prophet Adam spoke in paradise. Moreover, it is the language with which Allah sent down the Qur’an. Hence, it is not permissible to cuss it or mock it.

The Arabic language is the best of the languages and it is the language of the best of the creations; our master Muhammad, Sallallahu ^alayhi wa Sallam. It is the easiest language to learn as indicated in the saying of Allah the exalted in Surat al-Qamar Ayah 17:

ولقَدْ يَسَّرْنَا القُرْآنَ لِلذِّكْرِ فَهَلْ مِنْ مُّدَّكِرٍ

which means as explained by Sa^id Ibn Jubair: << We (Allah) made the Quran easy for memorizing and recitation >>.

However, due to the mingling of non-Arabs with Arabs some who did not know started saying “the Arabic language is difficult”; this saying is prohibited. Indeed the Arabic language is the best, easiest and most beautiful language and it is the language of the Glorious Quran which is the best of the Revealed Books that preached, Allah is clear of imperfection and called for Islam. Hence, it is prohibited to cuss, belittle, or dispraise the Arabic language or even a single letter of it such as the Alif or ^Ain or other.

Also, it is prohibited to cuss the Arabic grammar– the rules and conjugations, because they facilitate understanding the Hadith and Qur’an. As well, it is prohibited to cuss the sciences of Balaghah-articulation and al^Aroud-poetry structures and other disciplines among the beneficial sciences of the Arabic language. The one who cusses the Arabic language and degrades it or cusses even a single letter of it is not a Muslim, because one has cussed the language of the Qur’an and a letter that is in the glorious Qur’an. Hence, protect your tongues from that and from every talk that is not beneficial.
Ibn Abu Shaibah, al-Hakim and others narrated about Ibn ^Abbas may Allah accept both of their deeds who said the messenger of Allah, sallallahu ^alayhi wa sallam, said:

أحِبُّوا العرَبَ لثَلاثٍ لأنّي عَربيّ والقُرآنَ عَربيّ وكلامَ أهلِ الجنّةِ عَربيٌّ

This means:  ‘Love the Arabic language for three reasons; because I am an Arab and the Qur’an is in Arabic and the mother tongue of the inhabitants of Paradise is Arabic’
Hence, be mindful and teach your children and others this important matter.