@jlptn1 There's a theory that babies' babbling is often interpreted as referring to things. This explains why short reduplicated words like /mama/, /papa/, /baba/, /dada/, /nana/, /tɕitɕi/, etc. refer to things babies are interested in, even across unrelated languages (which makes borrowing unlikely).
In this case, parents in multiple cultures seem to have interpreted /tʃitʃi/ as "breasts", i.e. "I want to be fed", presumably by coincidence, and it got established as a word in both Japanese and Mexican Spanish.
For example, these noises are often interpreted as referring to parents, e.g. /mama/ for "mother" in English and Chinese, /papa/ for "mother" in Japanese (subsequently sound-changed to /haha/), ....
@Flaw Mmmm, if someone says 丸がかいてある, I won't be sure if it's a wobbly/fuzzy/sketchy/perfect circle. In case of 円がかいてある, it's definitely going to be a clean, perfect circle ○. I think 丸 is a superset of 円.
In any case, 丸 is more frequently used in everyday conversation for referring to circular shapes.
Interesting list of hard-to-read kanjis, brand names, person names and tech terms: http://www.1101.com/yomenago/sakuin.html
@gibbon It is true that kanji 円 can also be read as まる, but 円 as a mathematical term is always read as えん. まる is not a mathematical term, whether it is written as 丸 or 円. I am sure that ento is talking about the reading えん of 円.
Every once in awhile there would be a very strong statement about "X is offensive in English", or "Y is unnatural English"... which would be blatantly wrong