Ramban mentions that among other aspects of how Moshe caught Pharoah's daughter's interest is that his cry sounded like that of an older boy.

In thinking further back about how Yocheved had been able to hide Moshe for 3 months I think this could provide an answer.

Anyone hearing the cries of Moshe as a newborn might have thought that it was the cries of his older brother Aharon.

I think this is true. I think that babies learn and imitate speech, even in the womb.

An example of this is when my first child was only three days old and I was putting a shirt on her. I could swear she said "don't." Then my husband said "Did she say "don't." And I said yes she did.