I know this is far from a record, but my huge Dark Brahma hen has only just decided to part company with her 9 very big chicks of 13.5 weeks. She was still breaking food up and offering it to the chicks who were starting on typical adolescent behaviour up until 2 days ago. Momma wandered off (she has been free-ranging with them since 5 weeks of age) and promptly went into an egg box where she sat for 3 hours and is already behaving as though she is ready to hatch another brood.(Obviously not her own!). I picked her up and checked her thoroughly....no parasites, good feathers and over 9 lbs in weight, so definitely fit for another 'sitting session'. So how long have others had hens with chicks?