To the OP and anyone else - if you can get up the front of the plane with your children, no matter what their age, then my view is do it!
My wife, 17 month old son and I are currently in the US having flown here about 6 weeks ago on our way to moving to Canada for a year (and to the poster who thought it was selfish to take infants on a plane, perhaps moving overseas for a job is one of the reasons people travel with infants). The 8 hour day flight from PER to HKG was actually harder than the 16 hour flight from HKG to JFK, since there was more normal time he'd be awake on the shorter flight. We flew J from PER and F on the long flight to JFK.
Two days before the F flight I saw we were the only passengers in Cathay's 6-person cabin, and was rejoicing. But on the day itself the entire cabin was full. I might have been imagining a few stares from other F passengers, but we had 1A and 2A, whilst the other four seats all share the other aisle, so we had our own space and even when walking about our son couldn't get near anyone else's suite.
He slept for 12 hours. Most of the FAs commented that they'd never seen a baby in first class before, but they all complimented us at the end for how amazingly well behaved he was. On the couple of occasions he started getting grumpy or fidgety, one of us just took him for a long walk down to the back of plane to show him how much less space he might have had
The key to any flight with an infant (and we've flown with our son on about a dozen flights to date) is to prepare for success. This means bringing plenty of food, toys, amusement, play school/sesame street on the iPad etc. New toys that he's never seen before are gold. It means planning flight times to coincide with normal sleeping times. And above it, it means accepting that you are not in F to sit down and enjoy a lovely degustation with matching wines before getting in a long sleep - it is to ensure your child is happy and quiet as much as is humanly possible. Anything else above this is a bonus.
It's much easier with one child and two parents I imagine. On all flights my wife and I usually take turns to eat meals, whilst the other one either feeds or entertains our son. Cathay F was actually a rare treat since he fell asleep soon after takeoff in my wife's seat, and she joined me for a meal in my suite
To those concerned their child with have a meltdown, I actually think that even if this is their personality, the odds are actually lower in J or F since they'll have more space and feel less 'controlled' because of that. Plus no matter how good a sleeper a child is, I bet they'll be better lying down than sitting up.