Wondering if anyone knows when it's consider safe to have blankets in the crib with baby?

we used to swaddle our baby but she got very active around 3 months and started breaking out and pulling the blanket over her head. we switched to the halo sleep sacks and they are wonderful. she is always nice and warm and she can't get out over her face.

http://onsafety.cpsc.gov/blog/2012/09/18/safe-sleep-bedding-pillows-safety-and-more/

the recommendation is when they go into the toddler bed

My son is 4 mos (as of today) and we've been using blankets on his since he was born. We've always made sure to just tuck them under him up at the top but now that's he's rolling and such, we just lay it on him but never above the armpits