refreshChildQuantity example

public function setQuantity(int $quantity): self
    {
        if ($quantity < 1) {
            throw CartException::invalidQuantity($quantity);
        }

        if (!$this->isStackable()) {
            throw CartException::lineItemNotStackable($this->id);
        }

        if ($this->hasChildren()) {
            $this->refreshChildQuantity($this->children, $this->quantity, $quantity);
        }

        if ($this->priceDefinition instanceof QuantityPriceDefinition) {
            $this->price = null;
        }

        $this->quantity = $quantity;

        return $this;
    }