You can presume that your kid will have roughly the same lifestyle, and emissions, as you over a lifetime - so having a kid is a decision of doubling your emissions.
We became vegetarians the moment we became parents. Not because I think our individual change will make a difference but because I want it to be a no-brainer for our kids to drastically reduce meat intake.
If you don’t want to raise kids, that is fine. But don’t act like having 1 or 2 kids is ruining the planet. It is not, it’s the way we live that is.