Can anyone direct me to bass fret finger stretching exercises for very small hands?

I have recently taken up the electric bass, a lefty of average size. My hands are those of a 10-year-old’s, and with the DVD I have, I am having trouble following the instructor when he says that the fingers should be on the 1st-4th frets. He has small hands, but they’re small hands for a man. His fingers can reach to the fifth fret. My pinky barely reaches the third fret, and when I do place a finger in the right position, the others want to come off the fretboard as if I’m a Victorian dowager with a teacup.

Are there exercises to stretch my hands and keep them flat that the guitar players of the collective can tell me about?