When will roaming be available on the Apple Watch again?

Set up cellular on Apple Watch - Apple Support

International roaming with your Apple Watch

With watchOS 9.1 and later, international roaming is available on cellular models of Apple Watch Series 5 and later, Apple Watch SE and later, and Apple Watch Ultra. 

To get international roaming on your Apple Watch, contact your iPhone carrier to add your watch to your iPhone cellular roaming plan. For international roaming to work on your Apple Watch, your carrier must support VoLTE and roaming. Not all carriers support international roaming on Apple Watch and coverage in other countries is determined by your carrier.

To turn on international roaming, open the Settings app on your Apple Watch. Tap Cellular, then turn on Data Roaming.

International roaming isn't supported on cellular models of Apple Watch that were set up using Apple Watch For Your Kids.

To cover the LTE and UMTS bands used around the world, cellular models of Apple Watch come in regional models for the Americas, China mainland, and Europe/Asia Pacific. Unlike iPhone, there isn't a worldwide Apple Watch model that supports all cellular bands used globally. Find out which carriers in your country or region offer cellular service for Apple Watch.

Cellular services are provided by the carrier. Carriers issue SIM or eSIM cards that enable roaming and other services. Apple does not restrict roaming. If roaming is not working, the SIM (eSIM) may need to be reprovisioned by your carrier.

Please make sure your daughter’s iPhone is updated to latest iOS and that any available modem firmware is updated. If issue persists, contact your carrier for support.

That’s a carrier issue and potentially a Watch issue. If your carrier permits it on Apple Watch, it roams, if you’re within the same country. The issue with traveling outside the country is the Watch may not support the wireless bands on the cellular network your carrier supports for roaming. It’s also possible that the bands in the country just aren’t supported by your model Apple Watch. So, while roaming is possible, there are multiple conditions that may prevent it from working. This can mean roaming works in one country, but doesn’t work in another. As an example I have no issue roaming in Canada with my US watch.