I'm writing on behalf of my sister who has a 12 and a half week baby boy. He'll fall asleep on her but then as soon as she puts him down he is up and crying/screaming. This happens both during the day and at night and she's exhausted. She's tried many things to get him to sleep in the cot - warming the sheets, swaddling, putting him down when he is already asleep etc. - but he still always wakes up. Has anyone got any advice?? Thanks so much.