Hmm interesting.... From reading different sources it seems that many people have travelled with an under 2 toddler in business class with them having their own seat.

Essentially the adults have their two seats and hold the child for take off and landing and when required... And the extra seat is used for the baby to sleep and lie down / play .

We have done this with other airlines before, just not delta ...

We have also done 3 economy seats with him having his own seat, without a car seat etc and its never been a problem .. Seems like it's all a grey area