Bring the broth just to a boil. Broth can be seasoned with star anise and/or galangal or ginger. Add the meat and cook that just until it's done. If using onions and/or mushrooms, add them when you add the meat.
Add the noodles, bring back to simmer and turn the heat off.
Serve in large bowls and let everyone add what they like from the garnish tray.
Notes
Rice noodles: You can use the thin sticks or slightly wider ones. They can be cut with kitchen shears to make them easier for kids to handle.
Almost anything but the broth and noodles can be omitted.
Gluten: Gluten is a protein found in specific grains (wheat, spelt, kamut, barley, rye). Other grains are naturally gluten-free but may have cross-contact with gluten-containing grains. Look for certified gluten-free products if you need to avoid gluten. Find out more about wheat and gluten substitutions.