When my children were very young, I think pre-school, the tablets and phones were a lifesaver!
Sure - you can do colouring, stickers etc.. but my children tired of these much quicker than it took for the food to arrive, and with no screens we had to rush our meals and leave quickly. Three year olds cannot sit still for long periods (certainly mine couldn't!)
When I gave my pre-school age children a screen in a restaurant it meant we didn't worry how long it took for the food to arrive, could enjoy our meal slowly, and maybe even have a coffee at the end of the meal! It was a far more relaxing experience.
Now my children are older, they don't bring any phones when we go to a cafe or restaurant, they are not allowed, but they have better concentration and can manage to sit still and wait for their food, and they are are able to have conversations around the table. So it's all fine.
I honestly don't see what's wrong with pre-school age children having a device at the table as long as the sound is off or they use headphones.
I sometimes think the people who judge this assume that these parents must be placing their child in a locked room in front of a screen 24 hours a day! Makes me laugh!
My children may have had a tablet at the table for lunch occasionally when out, but they also swam, played football, did arts and crafts, built Lego, climbed trees ..... Now in yr 8 and yr 6 their early exposure to a screen on occasion when in a restaurant seems to have done them no harm! Both are kind, intelligent, thoughtful children able to hold good conversation around the lunch table!