When to Stop Sleep Sacks: Safe Sleep practices for infants include the use of sleep sacks to prevent loose bedding from covering their faces. As infants grow and become more mobile, they may start rolling or moving around in their sleep, which could cause the sleep sack to bunch up or cover their face. It is generally recommended to stop using sleep sacks when infants show signs of rolling or when they reach 6 to 9 months of age, whichever comes first.