Investment is a loaded word though. The immediate connotation is expensive monetary investments, like college and private school. It's true that you should cut back on these. But in some sense, these can only be the binding constraint if you're very forward looking. By the time you're in a position to actually decide whether to pay for your child's first year of college or just let them have some student debt, it's highly likely that you're long past the point of deciding whether to have more children.
No, the insidious aspects of investment are those in the very early years of a child's life - waking up every two hours to feed them, dealing with crying and tantrums and poopy diapers. And the reason they bite the most is that by the time you're thinking about having another child, many of the worst bits have just passed. The child is now two or three, and you have just started to get the feeling of having gotten over the top of the hill. If you simply stop now, you never have to deal with that phase ever again.
Look, I sympathise with this feeling. I think everyone does, including parents who had lots of children.
But the mystery is still the time series. Your great grandmother had 7 children, and managed to rub along just fine. Not only that, she did so while washing every dish by hand, washing every shirt by hand, cooking every meal that the household ate, and on a budget a fraction as large in real terms as you have.
Hence the mystery - how did it all apparently get so much harder? What is it your great grandmother knew, but you don't know?
I suspect that one largely unremarked upon aspect is that your great grandmother started much earlier, in her early 20s. All that energy you put into partying into the wee hours and running on a treadmill? She put it into getting up in the night to feed children, and chasing after them by day.
My guess for the biggest factor is social support structures. Both sets of grandparents living nearby, for instance. Trying to make up for that with hourly babysitters is like running a one man lesson in Ronald Coase's theory of the firm, where you find out that a lot of things are considerably harder to contract on than you thought. Friends and neighbours with lots of children, whom you could turn to when things were tight. Now nobody knows their neighbours.
So, to the extent you can do this stuff, it's totally worthwhile. Fly in your parents for a while, if they don't live nearby. Try and do like the Mormons do, and make good enough friends with people nearby that you can do shared babysitting things.
These things are hard, though. If your parents live on the other side of the country, or the planet for that matter, rearranging your life or theirs to remedy this distance is probably not practical advice.
But there's another aspect to it. Culturally, a hundred years ago everyone was just far more comfortable with radically increased autonomy for children, and far less moment-to-moment supervision of what they were doing. I remember the Daily Mail depicting this visually in a quite arresting manner, showing how far different generations of Brits were allowed to walk.
Rotherham, Rotherham... where have I heard that name before? Hmm, maybe it's not just cultural norms.
But at a very young age, when children require full time care, was it always this hard? Is it possible to just...do less? Let the kid cry? Let the kid walk around on their own more, at a younger age, without being supervised, even if they sometimes cut themselves or bump their head? Let the kid figure out how to put themselves back to sleep? Let the kid play with the toys on their own, rather than expecting to have one or other parents joining them all times?
Parenting plans, like Mike Tyson's quip about boxing plans, last until you metaphorically get punched in the mouth. It's easy to say in the abstract that you'll just be a little bit more distant when the kid starts demanding attention, but another thing altogether when the kid is screaming their head off. And for someone like me, who has zero kids, there's an inevitable aspect of cheap talk to all this. If someone else has a troublesome child, maybe it's just genetics, or nutrition, or something else hard to fix in the short term. Maybe if you had their child, you'd act the same way.
Still, there is one metric that I think shows that reductions are possible. Namely, the inevitable decline in attention that occurs in nearly all parents between their first child, and their subsequent children.
For the first child, you're worried about everything going wrong. You're taking endless baby photos, and reading to them all the time. You're doing all sorts of stuff. By child number 4, you just don't have time for that any more. The child is crying? Is this a problem? Depends. Are they fed recently? Is their diaper clean? Are they sick? If the answers are "Yes, Yes and No" respectively, then no, it isn't fundamentally a problem. It's unfortunate, but it's okay to just close the door and let them figure it out. They'll work out just fine.
Hence the minimum viable Holmes advice for new parents:
Aim to bring a fourth child attitude to your first child.
Ask older parents - do they think their fourth child turned out much worse because of the lesser attention paid? Or do the younger children mostly tend to appreciate the more laid back attitude that parents took, and which older siblings are often jealous of?
Not only is it doable, for many aspects of parental involvement it's not even clear what the sign is for the effect of the extra effort.
Of course, there's one caveat here. There is non-trivial evidence of birth order effects, whereby first-born children tend to outperform in life (I trust Scott Alexander probably as much or more than the social science literature on this stuff). At least some of this effect is probably the extra efforts their parents are putting in.
That said, there's two responses. First all all, this just says that there's something on the revenues side of the ledger. This doesn't mean that the whole project of the extra effort for the first child is actually NPV positive for anyone involved. Indeed, given the extent of the extra effort, finding zero birth order effects would be evidence of a massive failure in rational parental investment.
Secondly, it's not clear how much of the effect of birth order is due to extra parental investment, versus just having more confidence by virtue of being bigger and stronger than one's siblings. It's probably both, of course. But any part of it that's coming from just sibling size doesn't require any investment, and is unbudgeable by your efforts in any case. I think the jury is still out on this one.
More importantly, suppose you believe that there might be an investment and/or confidence channel. If you're worried about this, just load up on the related investment/confidence effect - birth month. It's also true that the oldest children in a kindergarten class tend to outperform in life, for a similar mix of reasons. They're bigger and more confident than their peers, and they get greater investment because teachers and coaches perceive them as more talented when they're young, when they're simply more mature.
So if you're a big believer in birth order effects signalling something important, just aim to have all your kids be born at the start of the school year. It costs you nothing other than delaying slightly when you start trying to conceive. It'll probably also go a decent way towards offsetting any effects of reduced parenting for the first child (and will be a likely benefit to later children, for no obvious cost).
And remember, the second you're tempted to feel guilty about this advice and plan, just bear in mind - you're thinking of the wrong counterfactual. The whole point of doing all these reductions in wasteful effort is so that you can easily and cheerfully bring one more child into the world, with a full complement of life's joys, sorrows and experiences. That is something to be proud of, not embarrassed.
Fourth children turn out just fine.
