Thanks for all the comments (even the nasty ones). Let's just clarify a few points.
1) It's a 6pm dinner - hardly past anyone's bedtime
2) There is no 'running around' havoc involved. It just doesn't happen. We've eaten out in restaurants since the kids were in their car-seats. This little one is a veteran of Roly's (both Ballsbridge & Dun Laoghaire) and a few other somewhat posh places from our travels around. There might be more frequent trips to the loo than the average punter. There might be a bit of chat with the waiting staff. There might be a raised voice or two.
3) In the very unlikely event of a total meltdown (it happened once before, in an Eddie Rockets as it happens), I just pick her up and carry her out. If absolutely necessary, we'll just go home early.
4) The reason for bringing her along is not because of a lack of a sitter. We are a family. We are celebrating a family occasion. She is part of our family. I will enjoy her company. Others will enjoy her company (and will distract and entertain her for short periods, so I get to relax too). I see that a big part of my job as parent is to create unforgettable happy memories for my kids, and to let them know that family is important, very important.
5) The family member who did the booking has checked with Shanahans (I didn't make the booking, so it thought it best to let the booker do the checking), and they have confirmed that they welcome children.
So if Shanahan's are reading this, get that 24oz ready, I'm on the way.