they arent mammels though, they dont have nipples.

they don’t get born at all, they get delivered by stork exclusively on blue moons. they’re probably magical creatures more akin to fairies than anything else. we don’t even know for a fact that they can die of old age.

besides, the presence of Smurfette falls entirely outside of their biology since she was created from blue clay by Gargamel, so including her in any argument is faulty to begin with.