Manual dexterity is usually less developed in
B. children who have not established a dominant hand.
Explanation:
While right handed children have a better motor development partly because of the sustenance by the factors of the society that lead the right hand way more than the left.
But even then, the left handed children generally have more capabilities in motor ability and are therefore having less asymmetries early on than the right handed kids.
It is the ones that do not establish a hand that are thus far behind in dexterity.