For many multilingual communities, children learn English alongside the native dialect. So, asking what their "first language" is doesn't really make sense.
For decades, missionaries have used the term "Heart Language" to refer to these native dialects because they can better speak to the individuals lived experience. Their native language is closer to their heart.
Local Girl Scout Carolee McCarty used this concept as she created a bilingual book for children in Ethiopia. And, she earned her Gold Award, scouting's highest honor, in the process.
Bad Days Don't Last Forever: Finding Joy When the Rain Stops in English and Amharic https://a.co/d/9095PBc
https://openheartsbigdreams.org/