There are many websites present on the net that provides free phone surveillance service. You can visit them and get your job done in notime.
Q: How do I do this with my child's phone?
You can use the GPS service to track lost child. So, if your child is going for a trekking or if he/she is out taking a stroll in the mall then you can use GPS enabled mobile phones to track his/her whereabouts and be always stress free!