Help on Handedness

How do you determine which hand is dominant for a child? We are really struggling with this since we would like to encourage writing with just one hand. Grace sucks both thumbs interchangeably, she usually eats with her spoon in her right hand, but she picks up finger food with either. She always kicks with her left foot, cuts with her right (because we have righty scissors) and would put crayons in the right hand to color on the right page and the left to color on the left page. Yesterday when she was "helping" Mark put the fence around the garden, she switched the hammer from her left to her right seamlessly. If she doesn't have a preference, I would really like for her to be right-handed because so many things in our world are set up for the majority who have a dominant right hand, but if she is a lefty, I don't want to confuse her either. If you have any resources or experiences to help me out on this one, please leave a comment...I'd like your input.