Babies younger than 1 year of age could potentially suffocate when they have a blanket in the crib or bassinet with them so don't place a blanket in the crib, bassinet or anything else the baby is sleeping in until the child reaches at least 1 year of age.
Babies don't really have the motor skills or ability to remove the blanket from their mouths and noses or roll over properly until at least 1 year of age.
So if the baby happens to roll over face first into the blanket then it could potentially cause suffocation.
To keep the baby warm you can put the baby in some footed pajamas which are also known as blanket sleepers.
That will keep the baby warm without having to worry about a blanket suffocating the baby.