The children of v are the all the vertices u such that v,u is in the edge set of the digraph D. So the children of a vertex v are exactly those vertices on a directed graph that v points to.
i1 : D = digraph({a,b,c,d,e},{{a,b},{b,c},{b,d},{e,b}});
i2 : children(D, b)
o2 = set {c, d}
o2 : Set
See also
descendants -- returns the descendants of a digraph