def children(args):
    """
    %prog children gff_file

    Get the children that have the same parent.
    """
    p = OptionParser(children.__doc__)
    p.add_option("--parents", default="gene",
            help="list of features to extract, use comma to separate (e.g."
            "'gene,mRNA') [default: %default]")

    opts, args = p.parse_args(args)

    if len(args) != 1:
        sys.exit(not p.print_help())

    gff_file, = args
    g = make_index(gff_file)
    parents = set(opts.parents.split(','))

    for feat in get_parents(gff_file, parents):

        cc = [c.id for c in g.children(feat.id, 1)]
        if len(cc) <= 1:
            continue

        print("\t".join(str(x) for x in \
                    (feat.id, feat.start, feat.stop, "|".join(cc))))
%prog children gff_file

    Get the children that have the same parent.