Does an e Sim work (Kids Whatch plan from Swisscom)

No, the Xplora XGO3 watch cannot be used without a SIM card if you want to use the full functionalities such as phone calls, messages and GPS tracking. The watch requires a SIM card, in particular the Xplora Connect SIM card recommended by Xplora, for optimal performance and to enable all functions such as GPS, phone calls and messages.

Without a SIM card, GPS tracking and other communication functions would not be available.