I'm usually quite tolerant when it comes to other people's children, and I do sometimes feel a bit sorry to see a stressed out mum or dad trying to control an unruly child. I've been there, so I do understand what it's like, but I do draw the line at the behaviour of some children in restaurants/cafes, and as a parent I wouldn't subject other customers to it.
I had two children, both brought up in the same way, both taught good manners (I tried!), both always ate at the table with us so they were totally used to it. One was an absolute angel (DD) who you could take anywhere, the other was an absolute horror (DS)!
I always remember one occasion on holiday with friends, them with their child and us with ours, going to a restaurant on our last day. The staff were very accommodating, moving tables for us, making space for pushchairs, bringing high-chairs, etc. All was fine until we began to order our meal, then DS decided to start his antics, and there was no stopping him! It was so embarrassing that I immediately removed him, and apologised profusely to other customers/staff. We all trooped out, went back at our apartment, and ordered pizzas instead!Lol I was mortified at the time, but we still laugh about with our friends today. Thankfully, DS grew up to be a thoroughly nice guy, and very well mannered, so I must've done something right!