I think those easy to make/instinctive sounds are a part of how our language is/was formed. I mean babies make that "ma...ma...ma" sound when crying, so you're not going to think, "hmmm I know we should call mothers, "wheelbarrow." This is of course my own entirely unscientific theory.
Re: I may sound crazy... But....
Elizabeth 5yrs old Jane 3yrs old
This, but it is actually linguistically correct.