I probably should have phrased it as "have less children" :)

My list was based on the book "How Bad Are Bananas" which goes into depth about the carbon emissions from various things, including children.

I'm not 100% sure that attributing the emissions of a child to their parents is correct 'accounting'. Maybe only their emissions until age 18? Still, all the emissions caused by that child and it's descendants would not have happened if it wasn't for the decision their parents made to create it. Accounted for this way, there is no doubt this is the most impactful decision someone in a developed country can make (that was the framing the OP used so I went with that) but it is not the most likely to happen, most practical or most moral option.