There is in a way. The correct sentence should be 'Maen nhw fel eu mam nhw'
Spoken Welsh often drops one of the pronouns of 'eu.........nhw' (their) usually the second one 'nhw', to give:- 'Maen nhw fel eu mam'
However some dialects will drop the first part to give 'Maen nhw fel mam nhw' as above.
This sentence was deleted a while ago, to avoid confusion, and apologies that it's still around to perplex people.