That's an extremely negative-sum way of viewing the world. Some individual humans (and even communities) can and have had a net-positive impact on the environment. For instance, did the parents of Greta Thunberg have a net-negative impact on the world by choosing to bring her into it?
When people implicitly say that bringing children in the world is necessarily a net-negative on climate, they're implying that their lifestyle is necessarily net-carbon-positive and that they just refuse to do enough to make their own lifestyle net-carbon-negative. Yet it IS possible to do so. I'm reminded of this Indian fellow who planted an entire forest pretty much by himself (although surely his wife/family also helped enable him to accomplish that goal): https://www.youtube.com/watch?v=i7i3QlMvsZs
...there are so many decisions one can make to cut one's carbon emissions to near zero. And some decisions can even make one's carbon emissions negative (some startups at Y Combinator, even... although there are more proven methods as well).
The most powerful thing as a parent is that you can help pass on your values to your children. Teach them (through example) how to live a low or negative carbon lifestyle and teach them the value of the environment and why the Earth must be protected. Plant trees. Make intentional decisions with lifestyle (mode of travel, living arrangements, diet) that lower carbon emissions, and explain these things to your children starting at a young age.
Because the world will NEED people with those values in the future if climate change will ever be addressed and eventually reversed without a collapse of human civilization. Because if everyone with a positive view of the environment and the need to fight climate change does not pass on that worldview to their children, BUT those who deny climate change and do not value the environment pass on their worldview to their children, then that is clearly not going to work out for those who value the environment.