declare function local:split($x as node()) as node() {
 let $name := $x/name/text() return
 let $tag := if ($x/@gender = "M")  then "man" else "woman" return
 let $sons := 
  for $p in $x/children/person[@gender="M"] return local:split($p) return
 let $daughters := 
  for $p in $x/children/person[@gender="F"] return local:split($p) return
 element {$tag} { 
  attribute name { $name },
  element sons { $sons },
  element daughters { $daughters }
 }
}
;

for $p in ./doc/person return 
<doc>{local:split($p)}</doc>