My 3 year old son has had bad breath for 2 days now and no matter what we do it does not go away?

bad breath
Leah asked:

What can it be from? We brush his teeth 3 times a day. He has no cavitys. His teeth a perfectly healthy. It seems like the smell comes out his nose too when his mouth is closed,Like when he is sleeping. He has never had anything like this before. Any suggestions on how to get rid of the bad breath? Oh and I cant give him mouth wash he is to young.
Thankyou.