I know this is a post on primary schools but I work in a senior school and will often have my mobile hidden in my bag or pocket.
Not so I can text my friends, arrange dental appts or a night out etc but for any emergency that might arise. My school is based on a very big campus and my childrens school twice in the past have left messages with the reception that one child is ill or had an accident and its never got to me! (although a room change to a computer suite did confuse the receptionist! for one of the calls!)
However I have had occasion where I've needed to call the SMT to come and remove a violent pupil quickly and when a girl fainted last year, hitting her head on corner of desk, an ambulance was called immediately (there was a lot of blood - although turned out to be small cut but she remained unconscious for quite a while even after ambulance had arrived) and reception was called straight after 999.
If your childrens teacher is texting constantly then yes there is a reason to communicate your upset with the school but really I don't think anyone would take your concerns of paedophiles and photography seriously. My school is covered by CCTV, lots of pupils and teachers have to use school cameras for projects, evaluations etc and pupils bring in phones (although they are handed in at start of day)
As staff, we have to protect ourselves as well as the children and 1:1 sessions have had to cease (for our safety too)and interviews, mentoring etc are now all done with another adult present too. Its a very sad state of affairs.
I can understand that some nurseries might start a ban on mobiles while staff work, These are very young children who are unable to vocalise what they have done at nursery all day, or who has been with them. They are often still in nappies or being potty trained which might result in accidents and so they are far more vulnerable.
I am sorry to hear that you had a problem with a carer in the past and I hope your children are all ok now. But please don't assume that all teachers, carers, nursery nurses etc are working in schools and nurseries with ulterior motives. these individuals who partook in this terrible crime were very sick individuals but most of us are in the job because we love to teach and we love the satisfaction we get from our jobs.