My sister-in-law noticed that her daughter had terrible breath when she drank Juicy Juice.
another thing that even kids with no teeth might benefit from a little kids toothpaste on the gums.
They need to stay hydrated as well. A child, or adult for that matter, that does not get enough fluids will get bad breath.
They will also get bad breath when they are sick...like runny noses and such.
Hope that gives you some help.