The Xiaomi Smart Kids Watch does not come with a built-in SIM card. You need to purchase a Nano-SIM card separately. Please ensure you use the correct Nano-SIM card, as using a card cutter can prevent the SIM card from being inserted or removed properly and will damage the slot. Additionally, the watch does not support hot-swapping of SIM cards, so you should restart the watch whenever you reinsert the SIM card.
Note:
When the watch is connected to Wi-Fi, the video call function will prioritize the Wi-Fi network. If the watch is not connected to Wi-Fi, the video call function will utilize the data traffic from the SIM card installed in the watch.