Quoting Ole' No Name:" A blanket ? I mean a thick one like the quilt that comes with the crib bedding ? My DD is 10 months ... [snip!] ... during naps and see what they do and she does fine. I just worry since I'll be sleeping and probably wont wake to check on her."
We used receiving blankets until they started to be too small on him, so around 3 1/2-4 months I think? Might have been sooner though, with the fleece material blankets and he loves being wrapped up. I make sure the blanket is snug around his body, his arms are usually free though when I swaddle him or he ends up getting his arms out regardless. He used to kick the blankets off when he was younger since it was too hot enough out that I wasn't that worried about it.
Now I wrap him up snugly in one of his fleece blankets that we use or use one of his big crocheting blankets a family member made for him and I just make sure that its folded down to fit around his body snugly to help give him security and warmth and he loves it. He knows how to uncover his face and knows how to roll if needed too, so I don't worry too much.
Only time I worry is when he decides to cover his face in the mornings with the blanket I drape over his body to help him to warmer at night or his monkey blanket/toy. He thinks its funny. lol