A baby should not have anything too soft including a stuffed animal in the crib with them until 1 year of age.
Babies lack the motor skills needed to move their bodies and head away from objects that they could roll into which can prevent them from breathing correctly.
The baby could roll there head into the stuffed animal and the stuffed animal could block there nose and mouth and cause the baby to have trouble breathing which could lead to the babies death.
A baby should not have blankets either in their crib until they're 1 year old at least.
You can keep a baby warm by putting the baby in blanket sleepers which will keep the baby warm enough throughout the night.