You need to edit the the canadopt function on your functions.php page. I edited it so that they can only have 5 at a time that are young & then they have to level some up before they can adopt more.
PHP Code:
$query = "SELECT * FROM adopts_owned_adoptables WHERE currentlevel < '4' AND owner='$loggedinname' AND isfrozen='no' AND item='no'";
$result = mysql_query($query);
$num = mysql_numrows($result);
if($num >= 5){
$canadopt = "no";}
Gives you an idea of how I modified it.
Sea