At current, only members of the same race may have children with each other, so human with human, elf with elf, Halfkin Fox with Halfkin Fox, so on so forth; interbreeding would be mixing the races, so Elf with Human, Harpy with Beastkin Cat, etc, and in the base game this is only done via unlocking the Breeding sow class and giving it to a female or futa character, at which point they can be knocked up by members of other races, however the stats will only take after the mother