Awwww! Cute baby!

Another vote for 4 seats. We do have a sticky thread on kids in premium cabins at the top.

One thing about being in economy with a toddler is that they often find "friends", either little playmates or grandparents who miss their own grandchildren... Plus, less stress if the toddler makes noise or cries. Business class passengers did complain about children quicker.

If you do opt for business, please sit towards the back, preferably near the restrooms. If you're up front, you get to walk by all those staring fellow passengers with your poopy and/or crying child.

Also, feel free to take a walk to the back when there is no service going on.

This is a bad age, as you've been warned. They are active and don't understand concepts such as "You can get out of your seat once we're in the air". They also can't be bribed!! Be sure to be well-stocked and have some "surprise" toys for those tricky moments when they don't want to stay in their seats. Just as the aircraft is leaving the blocks, whip one out for each child. Ohhhh new toy! Distraction until you're in the air (and can't get kicked off the plane for not controlling your toddlers!)