Right here. This is where it all started.
My little cutie started shoving things into her (regular) sleep sack during nap and bedtime - stuffies, her arms, and even her sippy cup would be in there, rolling around at the bottom. Eventually she wanted her things back out, so she started figuring out how to remove the sleep sack, and got really good at it.
I mean REALLY good.
I didn't enjoy the sleep sack removal, as it inevitably resulted in a cold girl crying in the middle of the night. Since I am a sewing pattern designer, I started creating new sleep sack designs in an attempt to prevent her escape.
First I skipped the zipper in favor of snaps at the shoulders, but she figured out how to open the stiff snaps. Houdini level 1.
Next I put the zipper on the back, but she managed to get that open too. Houdini level 2.
Above is an early prototype of what eventually became the right solution. But this one had a flaw - it was too loose in the leg cuffs, allowing her to pull her legs up inside the suit and push her way out through the crotch....
Yes, that is correct. She ripped a giant hole in the fabric, while attempting to get her beloved stuffies (which she had put in through the sleeves) out of her sleep suit. Houdini level 5000.
Below is the sleep sack that eventually contained my little escape artist. It has a zipper that starts in the middle of the back (in that hard to reach area), with a stretchy cover over the zipper tab. To put the sleep sack on, you open the zipper all the way to the bottom and then put them in through the opening, and pull the neck hole over their head.
This design is available as a PDF sewing pattern called the Stylin' Snuggler, with an add-on for what I call the "Houdini Proof Method". The add-on includes the back zipper installation method, plus an extra low harem crotch option (for those who like foot openings) to accommodate putting it on over the head. The pattern is full of beginner tips and easy to follow - it was successfully tested by several beginners who had never sewn a zipper before!
Epilogue: My daughter has finally outgrown this stage, but before she did, I got smart and did something I should have done ages ago. I hacked the Stylin' Snuggler to include a large pocket on the front for her stuffies and such. She adored it!