I have been hearing some of David Benatar's antinatalist arguments recently, so have been thinking about this. People readily dismiss his case, but don't in my experience then make a positive case, like you ask for.
There is a sneaky universalising that goes on, whereby suffering, pain etc are considered universal and objectively meaningful, but meaning and purpose aren't - that's inconsistent. It seems to be they are the same kind of thing - judgements or reactions for navigating the world.
The population in developed countries is generally dropping rapidly, except in immigrant communities. Female education, good birth and infant care, availability of contraception, look to give birth rates like Japan. However, climate change and resource use are overwhelmingly driven by those stabilising or declining developed world populations, so.
That draws attention to culture. We can impact our culture in many ways, as active citizens through participation, and through pursuasion abd influence etc etc. But, probably no cultural impact we can have is more impactful than that we have through having a family. Through that, we institute a mini-culture, with a particular capacity to spread. If say we focus a family on reducing climate & resource impact, that can help lead a change in the next generation. This is the most poweful impact most of us can have, if done well - or, badly..
You can't justify having children if you don't think you will be a good parent. Having sufficient resources, that may be more ambiguous & based on optimism, but realistic appraisal has to help.
I am deeply suspicious of the urge to have objective meanings. It's like approaching the world with your eyes closed, having already decided what to see. Given the idea of all meaning being 'subjective' (subjective like say, Indra's net!), what is good comes down to what we have the intelligence to argue for coherently, and the passion and fortitude to believe. And, if that makes us more adaptable and resilient, it will be more likely to survive, along with adherents.
Being human is challenging, full of pitfalls and pains. But we have the scope in each of our lives, to be among the happiest and most fulfilled animals. It is sad we are so damaging the natural world right at the moment we can truly appreciate it. If we have found happiness and fulfilment, and we truly think we can help others to, we should say yes to life, and pay forward the care and support we had as children, to the next generations. Who can continue the task of healing & understanding the world.