It seems that the word "mom" derives from "mamm-", Latin for breast. I have actually heard it told that the Latin root "mamm-" derives from the baby's first natural sounds, though I cannot attribute this.
Interestingly, the etymology for "dad" states that this word is "nearly universal and probably prehistoric", an idea that corresponds nicely with the etymology for "mom". However, in my own language this word is not used for father, but rather we say "aba". In fact, my own empirical observations raising children lends to the idea that babies say the "a", "b", and "m" sounds, but not the "d" sound. Therefore I suggest selection bias towards whoever decided that because his culture encourages babies to say "d" (because they expect it) and that the baby then makes the sound.
How established can an etymology be, and how is one challenged? Is there a canonical etymology of English words? What other words have disputed etymologies? I know that I could write to the author of the website etymonline.com but I am more interested in understanding the process of creating and challenging etymologies than in correcting any inaccuracies.