I wantd a pattern for a sleep sack for my newest grandson. After looking at several options and finding nothing that satsified the criteral outlined by his mother, I decided to write my own.
This sleep sack uses DK weight yarn instead of worsted weight producing a nice spring, fall, or air conditioning option. It is worked from the top down in once piece so it is easily customizable and has a separating zipper inserted “upside down” allowing only the bottom portion to be opened for diaper changes. This was by request. My grandson received a commercially produced sleep sack with this feature and his parents loved being able to change nighttime diapers with minimal disturbance. You can always change to a traditional zipper inserted properly or knit a button band with buttonholes.( If you choose the button option simply omit casting on extra front edge stitches on Row 9 then pick up and knit the button/buttonhole bands in place of the zipper reinforcement. But knit this band before joining to work in the round at the bottom of the bag!)
Please be sure to download V3. It is the most recent version of this pattern!

Measurements are based on the Yarn Craft Council chart of standard measurements.

The sample was made using instructions for size 12 months and used 2 entire skeins of Baby Marble. Calculations indicate that the size 6 months would use a little over 1 skein and size 18 months would require about 2 and a half skeins but these sizes have not been tested.

If you find any errors or have any questions, please let me know!