Lots of young EAs are struggling with the issue of whether, when, where, and how to have kids, and whether becoming a parent will undermine being an Effective Altruist, in terms of opportunities costs such as career, time, energy, money, focus, and values.
For whatever it's worth, I'm happy to answer any questions you might have about parenting -- its pros and cons, ethics, practicalities, etc.
Background: I'm a 57-year-old dad; I've raised a 26-year-old daughter and a 6-month-old baby. I've also helped raise a teenage step-son, and I come from a big, close-knit family (I have about 30 cousins.) I've lived as a parent in the US (mostly), UK, and Australia. I'm also a psychology professor who's taught courses on parenting-relevant topics such as behavior genetics, educational psychology, evolutionary psychology, human intelligence, evolutionary game theory, and decision making. I've been involved in EA for the last 6 years, and I have a pronatalist orientation, with an interest in population ethics, reproductive bioethics, gamete donation, and cognitive and moral enhancement. I'm not an expert on every practical or scientific issue about parenting, but maybe my perspective could be useful to some EAs.
Pete -- I'd say with babies, most of the frustration comes from trying to multitask when it's not feasible, being anxious about why baby's crying (which gets reduced a lot with subsequent babies), and feeling like one 'should' be doing work stuff when it's not possible. If you don't sleep train a baby, you also end up sleep deprived, which makes you irritable and frustrated. On the other hand, the happiness is very frequent and strong (assuming baby is healthy and well). I'm naturally quite introverted, dysthymic, and irritable, but being around a happy baby makes me playful, delighted, and grounded; often I've been smiling so much at the end of the day that my face muscles hurt (which rarely happens around adults.)
Regarding thinking clearly, the only real cognitive deficits from parenting come from sleep deprivation (which is mostly avoidable), and from having a bit less time for self-care in terms of exercise, nutrition, nootropics, and cognitively stimulating socializing.