If you want true water transfer decals, Testors makes a "custom decal system" available at Walmart and other places for about 5 bucks. You use an inkjet printer to print the image on the decal paper, then spray on a clear coating. When it's dry, you dip in water and apply---just like you're doing a model car/airplane. Only bad thing I can find is the decal paper is about 5x8---but the kit comes with two sheets.
I did a window decal for my truck and was REAL happy till a hard rainstorm beat it up a little. I would suggest clearcoating over the decal if it's placed on, say, a tricycle or maybe a pump that would be exposed to the elements.
btw, that trike looks KILLER