Does LO need to be able to roll over both ways to be safe in a sleep sack? My LO can only roll from back to tummy, and doesn't know how to roll from tummy to back, so I'm worried that she'll get stuck on her tummy if she rolls over in the sleep sack.

Our ped also suggested to not use a sleep sack yet until she can roll both ways, but it seems like most people use the sleep sacks before LO are rolling both ways.