Balasree Chisim cannot speak Mandi properly and often incorporates Bangla words in his native Garo language. His elder brother Sagre and sister Aski can speak Mandi but do not use it unless someone talks to them in that language.
"This is their condition although they were born and brought up in a Garo village in Madhupur," Babul D Nokrek said about his children. "But the case with those living in the city is the worst," said the teacher of a school in the capital.
"It seems that my youngest son, who is just five, will not be able to learn pure Mandi. The other children--even those living in Madhupur--will also meet the same fate as in schools they are taught in Bangla and everyone around them speaks in Bangla" Babu said.
Not only Babul D Nokrek, people from other indigenous communities, including Chakma, Tripura, Hajong and Santal, living in the city or in areas where the majority speaks in Bangla, are anxious that their children will not learn their native tongues.
"Both my five-year-old son and nine-year-old daughter understand Santal language but they cannot speak in it," said Daniel Hasda. "They are good in Bangla and English."
These indigenous guardians said they are compelled to teach their children in Bangla so that they can compete with the Bangla-speaking students at school. And because of this their children are losing interest in learning their own mother tongues.
They said if the government takes initiatives for primary education in one's mother tongue--at least in the densely populated indigenous areas--then their children would not forget their mother tongues.
"We have our own alphabet but most Chakma people cannot enjoy our literature as they did not learn to write and read Chakma letters. They can, however, speak in it," said Trijinad Chakma, a student of Dhaka University.
Trijinad is one of the indigenous students who have published posters of Chakma alphabet to promote their language on the occasion of the International Mother Language Day today.
The Marma people also have their own alphabet. The Monipuris once had their own alphabet but now they use Bangla letters for writing. Other communities including the Bom, Garo, Hajong and Mro use the Roman or Bangla alphabet for writing.
A recent research shows that four indigenous languages--Bangli, Kurmi, Rajbangshi and Bhojpuri--out of 68 are forgotten now because of negligence and lack of practice. Nobody now speaks in these languages although people from these communities are present in the society.
The research conducted by Mohammed Rafi, a teacher of BRAC University, shows that 51 indigenous languages including Bede, Pahari, Bagdi and Sardi are threatened with extinction.
Sohel Hajong, general secretary of Bangladesh Adivasi Chhatra Sangram Parishad, said most people of their village in Sherpur do not speak in Hajong language.
"Each of our villages has around 10 families. Being a small community, we are becoming the victim of the majority of Bangla language," he said.
The indigenous people have long been demanding primary education of their children in their mother languages, but not much has been done so far.
Only two non-government primary schools in Godagari upazila of Rajshahi are teaching in Santal language.
The first school to teach in Santal language was opened in 1999.
"A total of 475 Santal students are studying in these two schools," said Rabindranath Soren, secretary general of Jatiya Adivasi Parishad, adding, "We run the school on donation."
According to the Chittagong Hill Tracts Peace Accord signed between the Janasanghati Samity and the government in 1997, three hill district councils were given authorities to arrange primary education for indigenous students in their own languages.
The Rangamati District Council arranged teachers' training on the Chakma alphabet. The Bandarban District Council translated textbooks up to class III in Marma and Bom languages but the students have not got those books as the council is yet to get the approval from the National Curriculum and Text Book Board.
With the help of Tripura Welfare Society, the Khagrachhari District Council published a book for children in Tripura language but that is also not being used at schools mainly because of lack of government initiative.
Mohammed Rafi in his book titled "Household Census of Small Ethnic Groups in Bangladesh" showed that 52.3 percent indigenous people want to teach their children in their own languages along with Bangla.
Many indigenous people are anxious about their next generations.
"Both of my sons speak in Bangla as all my neighbours are Bangalee and the medium of education is also Bangla. They did not learn Tripura...They are not even interested in it," said Dipol Tripura living in Feni.