I fly first class at least half the time (Is that frequently enough?).
But the point is, it doesn't matter where you sit on the plane, the following applies:
I don't care who sits with me as long as they don't smell or be terribly disruptive. A baby crying and fusing for a few moments here and there is OK. A child who wails through an entire flight is not, nor is the parent who sings incessant stupid babbling songs to try to quiet the child (I think I'd rather hear the crying). Nor is a child who kicks the back of your seat. Or a drunk and beligerent passenger. Or cheerleaders singing Christmas carols through the entire flight--they needed a good punch in the head--enough to knock out a few teeth.
If you have a generally well behaved baby, no problem. Don't change the diaper on the seat (gross!!!), make sure you have a bottle for take off and landing. And talk to the pediatrician before you go about giving the kid some Benadryl to avoid ear pain.
And if you have terrors for toddlers, drive. That's just common courtesy. My son was a terror of a toddler. We didn't fly anywhere for a LONG time.
And as the other poster said, buy the kid a ticket. They will be safer, and they will also feel more secure int he seat taht they are used to traveling in.
Anne