I'm not going to claim having children is "rational", but to judge it by the happiness of "caring for children" is about the same as to judge quality of food by enjoyment of doing the dishes. This is very one-dimensional.

Moreover I actually think it's foolish to use any kind of logical process (such as reading this study) to make decisions in this area except for extreme circumstances such as not having enough money or having genetic diseases.

The reason for my attitude is that I think besides the positive upsides to having kids (there are many, if you're lucky) there is a huge aspect of regret minimization involved; it seems to me Nature choose stick rather than a carrot here.

ETA: I should perhaps say short-term carrot and a long term stick