That's what he calls bananas. Not sure where he gets it from.
I'm running it through google translate. One thing to keep in mind, and this is actually something someone on here (I forget who) pointed out to me, that we may not be hearing the word correctly, or know how to spell it since it is foreign. In any case, I'll paste results I think sound close to "manyas." I will say that going through it, "bananas" seems to be a fairly universal word?
Hausa: Ayaba. Mostly mentioning depending on how he says "manyas." (You mention the "y" is definitely in there.)
Hawaii: Maia.
Maori (New Zealand): Panana.
Samoan: Fa'i.
I kept the Samoan and Maori because it's possible that's leading somewhere. They are all Pacific languages same language, there's something about "Manyas" that sounds like it comes from one of the Pacific Islands. Keeping in mind that google translate doesn't cover every single language. Of course, I don't think there's a lot of moose running around Hawaii, but it could be another life...
Welsh: Manana or Mananas.
I wasn't able to find any cases with cars and moose either. Most of them seem to have had happy endings, or at least non-fatal ones But keep listening and looking, and see if he indicates any specific location, too.
(Also, I wonder if there isn't a fruit or even an object similar to bananas that he's remembering? How old is he? Young enough to maybe confuse words? Could simply be that "Manyas" reminds him of something that doesn't necessarily have to do with bananas.)
ETA: Oops, re-read and saw you mentioned that he's three. Does he mix up words generally? I believe some kids do even at that age, but I'm not really sure.