I was rushing to post that Redbud has heart-shaped leaves, then realized you wrote that they don't have leaves yet.
OK, well, I tend to think my redbud seedlings (I have 2nd year seedlings -- mine are Cercis canadensis
)have more reddish mahogany-colored bark than a typical flowering dogwood (Cornus florida
) (I don't have seedlings to compare to) which I tend to think has grey bark. Dogwood buds should be more developed at this time of the spring than redbuds' with a more round appearance compared to redbuds' pointy ones.