My son’s language background: When he first started talking (from just under a year to about 20 months), his exposure and preference was French, followed closely by English, then Spanish. Somewhere about 8 months ago, when he was 22 months, it transitioned to Spanish, followed by English, trailed by French. Now, at 30 months, his preference and exposure is based mostly in english, followed fairly closely with spanish, then trailed by french. In addition to these languages and being exposed to ASL since birth, his ear has also been consistently exposed to Japanese and most recently to Chinese too, resulting in spontaneous song and dance or counting in these languages. We don’t speak either of these at home, and he hasn’t yet started his playgroups to hear them live - his exposure is youtube based. So, that’s his background.
While visiting family, my grandmother told him in spanish something along the lines of “make sure to keep your shoes on so you don’t catch a virus through your feet!” she repeats this to him quite a bit because she’s very tidy, organized, clean, etc and insists on order … being barefoot is a no-no for her, so shrug whatever, she’s great-grams and it’s not hurting anything.
Well, last week, I noticed he had an obsession with beetles and being certain that beetles didn’t get his feet. Thanks to ybcr, i think, he knows what beetles are. It suddenly occurred to me that the way virus is pronounced in spanish by my grandmother, it DOES sound like beetles! All this time, he thinks that she’s telling him he has to put his shoes on so that BEETLES don’t get to him! lol. when i realized this, i enunciated 'VIRUS" in spanish, while speaking in spanish, so that he could realize that it is a different word. It reminded me of a post i read where the little girl would hear a word and run back asking for the spelling of it to ‘see’ the difference, even though it sounded the same to her.
Growing up, I recall not hearing things exactly right in various languages … even as an adult, learning a new language, it’s as though my hearing is turned off to certain sounds and inflections until i’ve reached a point of exposure with the language and then i can actually HEAR … so, it was neat to have this ‘ah ha!’ moment and realize my son does it too! it made me wonder if this is how it is for children as they start hearing their first languages - a sort of ‘charlie brown’s teacher’ at first and then, finally, clarity.
Does anyone else have multilingual experience to add to this thread?
This recent experience has just added to the realization of how important it is for us to keep our languages separated in the beginning to help the brain compartmentalize them appropriately and hear their distinctions clearly.
this is more of a rambling thread. 
i hope it made sense outside of my head!