Heres a couple of really early concept sketches for the children of the worms warbeasts:
Heres a pic of the children of the worms main cavalry. The Larval from of the Worm has limbs but as they grow they slowly change through several forms before reaching their final state.
And heres the final form. Bereft of limbs the great worm is a smaller version of the great devourer who resides in the southern deserts. With the ability to bestow the gift of unlife these are the harbingers of the children of the worm and are worshipped by their unliving minions as avatars of their dark god.
These are just a couple of really early thumbnails and I hope to really develop the concept which will also eventually include some warbeasts that fall between the size of the cavalry larva and the mighty worm. Also in the works are a couple of different infantry units and various characters. Hopefully the existing images will give you a general idea of what the devourers children will look like!
All the best!