Kids are cheap. All you really need is food and people.
Schools and car seats and houses are expensive, but if a generation has tons of kids, you'll have the manpower to make those things in 15 years.
Russia is kind of fucked right now and not only in demographic decline, but making it worse by killing half their young people. Will they pull out of it? Probably not.
But can they afford it? They absolutely can. And it's bad news for the rest of the world if they do. Don't underestimate this move. Especially because China is doing the same.