When I try to change the max baby count to say 8, it still produces 20.
Is there a minimum number for babies ??

Is there a minimum number for babies ??

No.

When I try to change the max baby count to say 8, it still produces 20.

So it spawns up to 20 after changing the value? Or do you get 20, then change the value to 8 and are left with 20 because they don't automatically despawn when you lower the limit?

It spawns 20 after changing the value in the mod settings before starting the game.
I take the mother out of my inventory, place her on the ground and still spawns the 20.

And if you go into mod settings while the game is going?

Factorio saves your map and player settings both outside game saves and inside. The map/player settings you change before loading a game are only used for newly generated worlds as default values. After creating and saving a world it has its own set of settings. So you have to change the settings while the world is running.

So you never changed your setting for the world you tested, and this is not a bug with Factorio or Broodmother.