safe for blankets?!?

Ann
When did you start letting your little one sleep with a blanket?? My husband wants to put one in my daughter's crib and I'm still so nervous!
She is 11.5mos old...she has used a sleep sack since about 3 mos old...she started walking at 10 mos.
Im sure she would be fine but I'm nervous, plus she sucks on her sack and pulls it up to her face when she's trying to fall asleep so I Know it's her comfort, I don't know.if it's time or how to transition...HELP!