Everybody have vastly different living expenses. Accounting for that expenses is the thing we're trying to avoid when replacing every kind of pension and benefit with one BIG. Why would we want to revert it 180 degrees when talking about children?

The whole point of what I wrote is avoiding the use of children as benefits-magnet by withhelding part of their BIG into savings. Pumping out 9 kids won't work because you'll get just 3 BIGs for them - the rest will go into savings. Then, having a child or two will actually be very financially rewarding because it's what is good for society.

BTW

"or more correctly - the basic marginal cost of adding a child to a household is negligible"

Seriously?? Are we talking about agrarian society or about modern countries?

You won't have your child in a studio, so naturally you'll need a very different home that costs (or rents for) a very different amount of money. And it all goes downhill from here. Mom or dad need extensive period of staying with their child off work, then find a babysitter and pay her, I'd say a first child accounts for more than +50% of a family spendings.

Basic Income should be for survival and basic necessities, nothing more. If a couple wants kids, one of them should work and make more money (the other one could stay at home). I don't think an entire family living off BIG is a good idea.

BIG should be able to offset their drop in ability to make money due to having a child.

"If a couple wants kids" - we have a problem right here. How is it suddently "if"? Somebody gave birth to both persons in that couple, and to their parents, and before that - why would they be the ones who break this chain?

They should surely have kids when they want to do so and they should not be put in disadvantaged position by having kids - which, well, does happen in almost every developed country and in many less-developed ones. Therefore, BIG for children.

Surely they should also work, but you know, their employer doesn't care whether they have children or not, so it should be compensated somehow.

Heck, I think women should receive BIG from the month their become pregnant. Delivering the baby is very financially-intensive process, no doubt.

I think having children is a choice, not an obligation nor a positive right (I'm not going to stop anyone from having children). Also, it's a pretty expensive choice. If others choose to have children, I'd prefer not to have to support them financially (through taxes).

In addition, as several other commenters pointed out, if you increase the BIG per child, you risk enabling people who have large families just to get the money. That much, much worse than asking people who want kids to provide for their own.

If having children is a choice that a sufficient number of people not take, you're going to starve when you get old.

Nobody asks whether you want to support the ill, the disabled and children, you just do that. You cough up cash because they are already there and you have no alternative.

You really don't.

I've recited my solution of preventing people who have large families to live off their children, it's kind of sad you don't bother to argue with it.

"You're going to starve when you get old" completely contradicts the basic premise of this discussion. We're talking about BIG in the context of an increasingly automated world, where fewer and fewer people need to work. This includes caring for the elderly (30 years from now, that might be completely automated). If I'll get my own share of BIG when I'm old, why would I care about children?

There's some choice involved in whether to have children... until you have them.

There's also some choice involved in whether you are making enough money to support your children -- but not that much.