We, like you, hate the idea of abusing trust and privacy.
However, children who want their parents to know when they're getting home from soccer practise, or see how far away their mother is when she's coming to pick them up, is quite a different scenario.
There are services that are as one-sided as you imply - the child doesn't have to 'opt-in'. Whereoscope is built quite differently.
I hate the idea. Absolutely hate it, and (No offense to those involved) hope and expect it to fail.