DD is still using both hands, but i always pass into her right hand, to encourage right-handedness (if she's left-handed i can't change it but if she's between the two i can), and she's gradually using it more and more over the left. She holds the fork in her left hand, but she manipulates the food onto it with her right. I think by the time they're 3 or so they're pretty much set in whichever hand is dominant.

Bx