When can we start putting a pillow behind our LOs heads when they sleep? Are there any pillows that can help prevent flat head?

There is no suggested age to introduce a pillow to your baby. General guide seemed to be after 12 months (at least) to reduce the risk of suffocation, and to choose one that is firm. Here's a great link that highlights points to looks out for when choosing a pillow for your baby: http://parent.guide/how-to-choose-the-best-toddler-pillow-for-your-child/