I think there is a big distinction between spying and monitoring your children. As parents, it’s our job to protect our children which have become even more difficult once they have unlimited access to the internet 24/7. They are susceptible to cyberbullying, can learn about sex, drugs, alcohol, weapons, and pretty much anything else in an uncontrolled environment.
There are monitoring apps, which can be downloaded to a child’s iPhone or iPad without their knowledge through iCloud and monitor everything that happens on the phone. I wouldn’t be comfortable using this kind of tech unless I felt that my children were in danger or could become a danger to him or herself.