I was in a cafe with DC and friend.
There was what looked like three generations of the same family 6yo , mother (about 30) and grandmother.
Got my attention because the mother told the 6yo (rather sharply) to sit down and behave.
I watched them (out of the corner of my eye) for the rest of the time I was in there - so 30 mins or so. The mother and grandmother spent the whole time on their phones- not even talking to each other - let alone talking to the 6yo. The 6yo had obviously finished eating/drinking, had nothing to do but fidget. The only time the mother spoke to the DC again that I saw was to tell them to stay in their chair.
I think I felt it more because I used to (still do) take my DCs out for a grown up treat of 'coffee' and cake ...it is something they love and we have a good chat, they get full on attention. (Before I get pulled up on it my DC was happily talking with their friend - not being ignored). I used to get taken out by my grandmother for the same and it is one of my fondest memories.
This child is just going to remember being ignored and bored mindless 
I know this is just a snapshot of their lives ...and I am being judgey but even so...AIBU to feel sorry for the DC? And to want to take their phones off them and jump up and down on them ?