Short answer: you can’t reliably “track a SIM number” yourself — only the carrier (or law enforcement) can triangulate a SIM’s cell-tower position, and they usually need account-holder consent or a legal order.
Practical route: use a phone-monitoring/family app (my go-to recommendation is mSpy — GPS/real‑time location, geofencing, SIM‑change alerts and history), but note it requires installing on the kid’s phone, the phone being powered on, and there are platform limits/costs.
Also talk to your carrier and make sure whatever you do is legal and you’re the account holder or have parental consent.