src/Models/SectionModel.php
public function getAllChildren(array $filter = [], $sort = ['LEFT_MARGIN' => 'ASC'])
    {
        if (!isset($this->fields['LEFT_MARGIN']) || !isset($this->fields['RIGHT_MARGIN'])) {
            $this->refresh();
        }

        return static::query()
            ->sort($sort)
            ->filter($filter)
            ->filter([
                '!ID' => $this->id,
                '>LEFT_MARGIN' => $this->fields['LEFT_MARGIN'],
                '<RIGHT_MARGIN' => $this->fields['RIGHT_MARGIN'],
            ])
            ->select('ID')
            ->getList()
            ->transform(function ($section) {
                return (int) $section['ID'];
            })
            ->all();
    }
public function getAllChildren(array $filter = [], $sort = ['LEFT_MARGIN' => 'ASC'])
    {
        if (!isset($this->fields['LEFT_MARGIN']) || !isset($this->fields['RIGHT_MARGIN'])) {
            $this->refresh();
        }

        return static::query()
            ->sort($sort)
            ->filter($filter)
            ->filter([
                '!ID' => $this->id,
                '>LEFT_MARGIN' => $this->fields['LEFT_MARGIN'],
                '<RIGHT_MARGIN' => $this->fields['RIGHT_MARGIN'],
            ])
            ->select('ID')
            ->getList()
            ->transform(function ($section) {
                return (int) $section['ID'];
            })
            ->all();
    }
Get IDs of all children of the section (direct or not).
Additional filter can be specified.

@param array $filter
@param array|string $sort

@return array