To freeze cooked meatballs for later use, let them cool completely, then transfer to a baking sheet. Freeze until they are pretty solid, 2 hours, before transferring them to a freezer bag.
To reheat, place the frozen meatballs in an ovenproof pan or baking dish and cover with foil. Bake at 150°C/300°F for approx. 30 minutes, or until hot all the way through.
If you have saucy meatballs to freeze, let everything cool then transfer to a freezer bag. Freeze until ready to use.
To reheat, place the frozen meatballs and sauce in a frying pan or baking dish and cover with foil. Bake at 150°C/300°F for approx. 45 minutes, or until hot all the way through.