Add milk, coffee, and vanilla coffee syrup to a 2 quart or larger Crock Pot. Stir.
Cook on high for two hours or until heated through. Make sure it doesn't boil! You may also heat it on low, but it will take a little longer to heat up. Turn Crock Pot to warm setting to keep latte warm for 2 - 3 hours. You can use low to keep it warm if your slow cooker doesn't have a warm setting, but keep an eye on it. Stir occasionally to make sure it doesn't scald.
Scoop by the ladleful into individual mugs. Top with whipped cream if desired. Serve.