I just wanted to give my two cents regarding the pearl clutching when strangers see a caregiver apparently too absorbed in their mobile device to focus on the child to their own standards.
I care for a child and do have to take texting breaks, and some days considerably more frequently than others. Not for a boyfriend, not for pals. In fact I rarely text in social situations other than "I'm here, meet me there" sort of logistical messages. The number one person on my texting list is the child's mother, second to that the backup caregiver. Mom sometimes needs to switch up plans on short notice, or wants updates on her child, who has been dealing with some health issues. This isn't always completed in a few messages.
On the parental side, I imagine some parents who may be looking at or speaking that device may have unfinished work that is being resolved via a mobile form of communication. Perhaps it is planning with the other family members plans regarding the rest of the day. If it wasn't for this admittedly compromised attention (assuming eyes are frequently on the child) maybe the parent would not be able to be home or take that outing at all in the first place.
When I text or receive texts, I still manage to keep an eye on the child and look up very frequently. I also tell him I'm communicating with his mother. My glances to him when he's a few feet away may or may not be detectable to others.
Just some food for thought before you take out a camera and point it at a stranger.