The part about confusing words between languages really resonates well with me. As someone who was raised in a household where two languages were spoken, I found myself speaking a combined language quite naturally—where I would midway sentence start speaking another language. Even now, grown up, I find that particular words come to me much quicker in a certain language. I think this quite healthy, as I believe it helps the development of the brain by making more neural connections between words, phrases, etc.

I hope your son does well with his English and Bangla, as well as Arabic, when he comes to that!