I experienced the same annoyance at the same situation once. There was not a peep out of the baby the whole time. I needn't have worried.
I also remember the time that DH and I went out for a last couple's meal before our first baby was born. I deliberately booked a restaurant that was not in a family area, for 8.00 or 8.30pm (can't remember now) so it was after the time that you normally get kids out in restaurants. I was so looking forward to it, I really was. It was mid week so I knew it would be a lovely quiet and relaxed atmosphere. I knew that was the last chance we'd have to enjoy a nice time out on our own for a very long time. Then 2 women came in with a baby of around 1 and stuck it in a high chair where it was unhappy and crying the whole time we were there. It went on for an hour, and made me more and more tense. They made no attempt to take it outside for a bit or even to pay much attention to it, let alone decide to skip a dessert or leave early for the baby's sake. The baby was clearly very overtired and would have been much happier at home in bed.
Having brought up 2 children since then, what they did baffles me. Why on earth didn't they have their evening catch up over a takeway at home and put the baby]s needs first? If they specifically wanted a meal out WITH the baby why didnt' they meet up earlier when the baby was less tired? Or visit a family-friendly restaurant with other children around?
I think people should tailor meals our to their own children, who are all different, as well as thinking of the impact on other diners from their poor decision-making. eg My first was fine in restaurants as a newborn, just slept. My second was a bloody nightmare, so we didn't take him to them till he was about 3. They were both fussy eaters as toddlers, and also not great at sitting still for long (same with most toddlers), so we chose not to take them out usually if we had the choice as it was stressful for everyone. As they've got older we have gradually gone from choosing earlier times at family-friendly restaurants with children's menus, to eating at fancier places at a later hour where they were the only children. They are impeccably behaved and it pisses me off to see people inflicting spoilt brats on others at inappropriate times of the day.
If you know your young baby is very unsettled after a certain hour go out earlier.
If your toddler can't sit still happily (and let's face it most can't) just go for a main course and make sure they have lots of snacks and toys to entertain them. Take them for a walk outside if they start whingeing. If your 9 year old is a very fussy eater don't take them to a high end restaurant of your choice where you know there is nothing on the menu that your child would like and who is going to moan and moan about not liking stuff.
I am more than happy to go to a restaurant with children in when in Europe, and people do always put forward the European example. But let's face it, in the UK we seem to produce a particular type of spoilt, whinging brat, usually with the type of parent who either finds them an inconvenience and barely pays them attention, or who is the adoring, over lenient parent who just thinks the world revolves round their child and there should be no rules. Please don't come to the fancy, coupley high-end restaurant that I'm at for a special celebration with my hsuband if you're one of those parents.
European families include their children in conversation, they pay them attention and keep them engaged. They pass them round the adults for cuddles so that the children don't get bored. They would also take them for a wander if they started being really disruptive to other diners, or to get them off to sleep in a pushchair. They just do it better.