Which vars do you mean exactly?

e.g.
control Menu(1) would be something like this:

foreach ($this->Menu(1) as $item) {
	if ($item->LinkOrSection() == 'section' && $item->Children()) {
		// etc. pp.
	}
}

Everytime I use "$this->Menu(1)" I get a Server Error.

All I want is to find out if the current page have children. But if I'm on home, the 4 links don't count.

Like this:

$page = $this;
$pages = array();
		
if($page->ShowInMenus || ($page->ID == $this->ID)) {
	$pages[] = $page;
}

$Parent = $pages[0]->record["ParentID"];

if($Parent != NULL && $Parent != 0 && !empty($Parent)) {
	$output = true;
}

Thats just reversed. There I have a "ParentID", poorly I don't have "ChildrenID".

Everytime I use "$this->Menu(1)" I get a Server Error.

Please set you environment to 'dev' mode. Then we could get a proper error message.

Director:
  environment_type: 'dev'

I really don't see what you trying to accomplish with your code. I've abbreviated your code to something simple:

if (!empty($this->ParentID)) {
	$output = true;
}

There I have a "ParentID", poorly I don't have "ChildrenID".

You don't have a ChildrenID, but an ID. SilverStripe will do the rest for you.

e.g. if we have two pages:

- ParentPage // ID = 12
    - ChildPage // ID = 13

foreach($ParentPage->Children() as $child) {
     echo $child->ID // 13
     echo $child->ParentID // 12
}

$parent = $ChildPage->Parent();
echo $parent->ID // 12

All I want is to find out if the current page have children. But if I'm on home, the 4 links don't count.

// if the current page have children ...
if ($this->Children()) {
    $output = true;
}
// But if I'm on home, the 4 links don't count
if ($this->URLSegment == 'home') {
    $output = false;
}

Well, sometimes I'm really stupid. Thats exactly what I'm searching for.

Just a little thing. If there's no children anymore then $output should be false. But thats the point where I don't know how I should do this.

If there's no children anymore then $output should be false. But thats the point, I don't know how I should do this.

The condition "<% if HaveChilden %>open<% end_if %>" will only be executed if HaveChilden returns true. But this will only do so if current page has children.

// default state
$output = false;

// if the current page have children ...
// ... else $output keeps being false
if ($this->Children()->exists()) {
    $output = true;
}

// But if I'm on home, the 4 links don't count
// ... else $output is either true if it $this has children or keeps being false
if ($this->URLSegment == 'home') {
    $output = false;
}

return $output // true or false

edit
I've made an error. "if ($this->Children())" will always return true, please use "if ($this->Children()->exists())" instead.

Thank you alot! That's exactly what I wanted. (: