"Among the earliest sounds babies make are the vowel [a] and a
bilabial [b,p,m]. sounds like ba, pa, ma should be made, but so should
ab, ap, am, etc. It is thought that this first word was interpreted by
mothers/fathers to refer to themselves e.g. narcissism !"
<weg>
At least it indeed is arbitrary as examples like Georgian mama
"father" vs. deda "mother" show. Nevertheless
such lallwörter shouldn't be used for historical-comparative purposes.
There also are other problematic cases like sound symbolism (e.g.
Dravidian a-, i-, e- deictic series), ideophones, or
items resistant to sound change for mysterious reasons like mata
in various Austronesian languages should have yielded reflexes like
**ma'a, but quite strangely didn't.
"What it does not explain is why some languages never went beyond
the 'baby stage' and got stuck with baby words while others, no doubt
because they were superior races, decided what they would invent new
words."
But... this applies to all historically attested languages! Of course,
except Neanderthals in mid 20th cent. films uttering avowedly primitive
sounding (like just one level above chimps) stuff like oogachakah
oogachakah ooh ooh ooh...
But maybe (at least traditional) Blackfoot parents were mature enough to
wait until their kids could say iksísst "mother, maternal
aunt" (besides a special vocative form na'á) and inn
"father" (interestingly without such a simpler vocative form),
the more as these are dependents and have to be obligatorily inflected
for possessor (an obligation I obviously violated here for simplicity's
sake). No seriously, maybe this has to do with the fact that
traditionally kids were expected to start speaking at a very much later
age. (Something immature Anglo parents might find desirable for less
noble reasons...)