How do I get my villagers to have more babies? They're 100% healthy, well-fed, there's enough food in stock, they have level 2 fertility - and yet every time I try getting 2 together, they run away because they're "too hungry to think about that".
Any hints?

Well, if they are too hungry that just means they are not well-fed.
In other words your foodsupply is not enough.
So pick more berries, harvest more crops or catch more fish.
If you have enough, they won't go hungry and then they will breed.

sounds reasonable
Though you should think that >300 food points is plenty for 9 healthy villagers...
Any idea what the "minimum" is?

at least 400 and you shouldn't get that message

Basically when the villagers start wandering about being curious about everything - usually a sign they got plenty of food.

I just kept putting them together until they shut up! Didn't take too long before they gave in, forgot the hunger pains and made more babies.