For all I know, my spawn might decide to work for Exxon Mobil.
If you believe that a small number of people will have an outsized impact, each person is a "lottery ticket".
If you believe in incremental progress then adding more people is likely to be "slightly positive".
If you believe that little progress will be made on per capita emissions (or that they may even grow) then each additional person is a carbon burden.
If a new person on the planet is born and goes their whole life without contributing to the cause and carrying on the current status quo of resource exploitation and fossil fuel usage, they will have made the crisis worse.
On the other hand, if within a generation or two each person is net carbon negative (through labour, taxes, innovation or other support towards climate efforts) then children born today will be helping to mitigate the crisis.
This is the "incremental" scenario. The plausibility of this depends on how you think system change happens and your assessment of what is possible or likely.
Besides, if it's feasible to earn enough money to offset your own carbon footprint (e.g. by paying for carbon capture), it's possible to scale the solution by having more children who then offset their own carbon cost and more.
The climate crisis and carbon in the atmosphere scales with the number of people available to solve it, as well.