Question
How do I trim 2 year old weeping willows?

Answer
There is no need to prune (trim) a 2 year old willow. Let it grow. I would not think about any pruning until the tree gets much older and larger. Then only if the over hanging limbs are in the way. At that time a light trimming could be done. The best times to prune willows trees are in the late summer or early fall. This variety bleeds sap, so it is important to prune when the sap is bleeding the least. I would think more of "giving it a hair cut" than the normal pruning of cutting off branches.